Exhibit 10.1

THIRD AMENDMENT TO STOCK PURCHASE AGREEMENT

This Third Amendment to Stock Purchase Agreement (“Amendment”) is made as of
June 1, 2009, by and among MasTec North America, Inc., a Florida corporation
(“Buyer”), MasTec, Inc., a Florida corporation (the “Guarantor”), Wanzek
Construction, Inc., a North Dakota corporation (the “Company”), Trust B under
the Amended and Restated Living Trust of Leo Wanzek dated February 2, 2000, a
North Dakota trust (“QTIP”), Janet L. Wanzek, a North Dakota resident (“Janet”),
Wanzek Construction 2008 Irrevocable Trust, a North Dakota trust (“IDIT”), Jon
L. Wanzek, a North Dakota resident (“Jon”) and Jon L. Wanzek 2008 Two-Year
Irrevocable Annuity Trust, a North Dakota trust (“GRAT”) (QTIP, Janet, IDIT, Jon
and GRAT taken together are the “Sellers”), and Jon, as Sellers’ Representative
(the “Sellers’ Representative”). Each of Buyer, Guarantor, Company, Sellers, and
Sellers’ Representative is a “Party” and together, the “Parties.”

R E C I T A L S

A. The Parties entered into a Stock Purchase Agreement dated October 4, 2008 and
subsequently amended such Stock Purchase Agreement on December 2, 2008 and
further on December 16, 2008 (the “Agreement”).

B. The Parties wish to further amend the Agreement as set forth herein.

AGREEMENT

NOW, THEREFORE, in consideration of the premises and of the mutual covenants
contained herein, the Parties agree as follows:

1. Capitalized terms used but not defined in this Amendment have the respective
meanings set forth in the Agreement.

2. Section 1.2 of the Agreement is hereby amended as follows:

The term “Substitute Escrowed Funds” is added to the glossary of defined terms
between the term “Stub Period Return” and the term “Survival Period” and the
location of such term is Section 2.3(b).

3. Notwithstanding the amount of Escrow Shares determined at Closing pursuant to
the Agreement, the Agreement is hereby amended to revise the definition of
“Escrow Shares” to be 776,699 MasTec Shares to be held in the Escrow Account
following the date hereof in accordance with the Escrow Agreement. Upon
execution and delivery of this Amendment, the Parties will execute and deliver
to the Escrow Agent all documents required by the Escrow Agent to release from
the Escrow Account all MasTec Shares in excess of the Escrow Shares (as defined
in this Amendment).

4. Immediately following Section 2.3(b) of the Agreement, the following
Section 2.3(c) is added:

“(c) Substitution of Collateral. The Sellers’ Representative shall have the
right, but not the obligation, to deliver Ten Million Dollars ($10,000,000) in
cash (the “Substitute Escrowed Funds”) to the Escrow Agent to be held in the
Escrow Account in substitution for the Escrow Shares. If Sellers’ Representative
exercises such right, then the Parties shall execute such additional agreements
with the Escrow Agent as the Escrow Agent may require to (i) release the Escrow
Shares to the Sellers’ Representative and (ii) take possession of the Substitute
Escrowed Funds.”

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The existing Sections 2.3(c) and 2.3(d) shall be renumbered 2.3(d) and 2.3(e),
respectively.

5. The parties acknowledge that the Final Closing Statement is attached hereto
as Exhibit A and agree that the Final Closing Adjustment is a positive Two
Million Two Hundred Ninety-Eight Thousand Two Hundred Twenty-Seven and No/100ths
Dollars ($2,298,227.00) all pursuant to Section 2.5. The Final Closing
Adjustment shall be paid by Buyer to the Sellers’ Representative seven (7) days
from the date hereof and shall include interest thereon from the Closing Date
until the Closing Adjustment Payment Date at an annual interest rate of five
percent (5%).

6. In calculating the Final Closing Adjustment, the parties classified the
Seaboard Receivable as set forth on Schedule 4.8, but in an updated amount of
$2,480,650 (the “Seaboard Receivable”), as an Excluded Accounts Receivable
because it was more than 120 days old as of the Closing Date. In addition, the
parties removed from current liabilities included in Actual Net Working Capital
$1,961,445 of accounts payable to subcontractors related to the Seaboard
Receivable (the “Seaboard Related Payables”). The Buyer agreed not to include
the Seaboard Related Payables in current liabilities for purposes of Actual Net
Working Capital used to determine the Final Closing Adjustment based upon the
assumption that no amounts will be payable with respect to the Seaboard Related
Payables unless the Company is able to collect on the Seaboard Receivable.
Accordingly, the Company shall retain all rights to the Seaboard Receivable and
the parties agree that pursuant to Section 2.7(a), (a) upon the Company’s
collection of all or any portion of the Seaboard Receivable, Sellers shall no
longer have any right to receive payment and (b) the Company shall not be
required to assign such receivable (nor shall the Sellers be entitled to such
assignment); provided, however, that should Buyer collect on the Seaboard
Receivable an amount in excess of the sum of (x) the amount due to be paid on
the Seaboard Related Payables, plus (y) all costs and expenses related to such
collection, and plus (z) the amount of any other Adverse Consequences in
connection therewith or the related project, the Buyer shall promptly pay such
excess to the Sellers’ Representative. The parties also agree that should all or
any portion of the Seaboard Related Payables be written off or reduced as
contemplated by Section 2.7(b), no amount shall be due or payable to Sellers in
connection therewith as they have already received the full benefit of valuing
the Seaboard Related Payables at zero. Sellers confirm and agree that all
Adverse Consequences of the Seaboard Receivable, the related project, including
those related to the subcontractor ECA, and the Seaboard Related Payables
(including any amount to be paid at any time to satisfy the Seaboard Related
Payables, and all fees, costs, expenses and other Adverse Consequences in
connection therewith) are Disclosed Matters to be indemnified in full by Sellers
pursuant to Section 11.2(d) of the Agreement; provided that Sellers’ obligation
to indemnify for the Seaboard Related Payables shall be reduced (on a dollar for
dollar basis) by the net amount of the Seaboard Receivable collected by the
Company, excluding any amount paid over to the Sellers’ Representative pursuant
to the 4 th sentence of this Section 6, after all costs and expenses of
collection.

 

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7. Section 7.6 of the Agreement is hereby amended to delete all references to
“MasTec Shares”. The second sentence of such section is amended to delete “at
the end of the Escrow Period” from the end of such sentence.

8. The Table of Contents is amended to reflect the sections and subsections
added to the Agreement by this Amendment.

9. Except as specifically amended hereby, the Agreement is and remains
unmodified and in full force and effect and is hereby ratified and confirmed.

10. Each of Sections 12.7 and 12.8 is by this reference incorporated into this
Amendment as if the text thereof was set forth in full herein and shall apply
fully to this Amendment.

11. This Amendment may be executed in counterparts, each of which shall be
deemed an original, but all of which together shall constitute one and the same
instrument.

[Remainder of page intentionally left blank]

 

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IN WITNESS WHEREOF, the parties have executed and delivered this Amendment as of
the date first set forth above.

 

Buyer:   MASTEC NORTH AMERICA, INC.   By:  

/s/ Pablo Alvarez

  Name:   Pablo Alvarez   Title:   Executive Vice President Mergers and
Acquisitions Guarantor:   MASTEC, INC.   By:  

/s/ Pablo Alvarez

  Name:   Pablo Alvarez   Title:   Executive Vice President Mergers and
Acquisitions Company:   WANZEK CONSTRUCTION, INC.   By  

/s/ Jon L. Wanzek

  Name:   Jon L. Wanzek   Title:   President Sellers:   Trust B under the
Amended and Restated Living Trust of Leo Wanzek dated February 2, 2000   By:  

/s/ Jon Wanzek

  Name:   Jon Wanzek   Its:   Trustee

[Signature Page to Third Amendment to SPA]

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  Wanzek Construction 2008 Irrevocable Trust   By:  

/s/ Jon Wanzek

  Name:   Jon Wanzek   Its:   Administrative Trustee   By:  

/s/ Kevin Gourde

  Name:   Kevin Gourde   Its:   Independent Trustee  

/s/ Janet L. Wanzek

  Janet L. Wanzek, an individual  

/s/ Jon L. Wanzek

  Jon L. Wanzek, an individual   Jon L. Wanzek 2008 Two-Year Irrevocable Annuity
Trust   By:  

/s/ Jon Wanzek

  Name:   Jon Wanzek   Its:   Trustee   By:  

/s/ Scott L. Anderson

  Name:   Scott L. Anderson   Its:   Independent Trustee Sellers’
Representative:    

/s/ Jon L. Wanzek

  Jon L. Wanzek, as Sellers’ Representative

[Signature Page to Third Amendment to SPA]