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                                                                     EXHIBIT 2.2


                            AMENDING AGREEMENT NO. 4

      THIS AMENDING AGREEMENT NO. 4 (this "AGREEMENT"), dated as of May 6, 2003
(the "EFFECTIVE DATE"), among Capital Environmental Resource Inc., a corporation
amalgamated under the laws of the Province of Ontario, Canada ("CERI"), and
American Stock Transfer & Trust Company (the "RIGHTS AGENT").

                              W I T N E S S E T H:

      WHEREAS, reference is made to the rights agreement, dated as of September
2, 1999, between CERI and the Rights Agent (as amended, the "RIGHTS AGREEMENT").
Capitalized terms used but not otherwise defined herein have the meanings given
to them in the Rights Agreement.

      WHEREAS, the Rights are presently redeemable pursuant to Section 23 of the
Rights Agreement;

      WHEREAS, CERI is its sole and absolute discretion desires to amend the
provisions of the Rights Agreement.

      NOW THEREFORE, in consideration of the mutual agreements herein contained
and other good and valuable consideration, the receipt and sufficiency of which
are hereby acknowledged, the parties hereto agree as follows:

                        AMENDMENT TO THE RIGHTS AGREEMENT

Effective as of the Effective Date, the Rights Agreement is hereby amended as
follows:

      (a) The definition of "Exempt Person" appearing in Section 1 of the Rights
Agreement is amended and restated in its entirety to read as follows:

      "Exempt Person" shall mean (i) the Company, (ii) any Subsidiary of the
Company, (iii) any employee benefit plan of the Company or of any Subsidiary of
the Company, (iv) any Person organized, appointed or established by the Company
for or pursuant to the terms of any such plan or for the purpose of funding any
such plan or funding other employee benefits for employees of the Company or any
Subsidiary of the Company, (v) Kelso Investment Associates, VI, L.P., a Delaware
limited partnership ("KIA"), and (vi) KEP VI, LLC, a Delaware limited liability
company ("KEP", together with KIA, the "KELSO Entities", and each individually,
a "KELSO ENTITY"); PROVIDED, HOWEVER, that the Kelso Entities shall cease to be
Exempt Persons in the event that either KIA or KEP becomes the Beneficial Owner
of any securities in the Company or its Affiliates, except securities
contemplated to be issued by the Company or its Affiliates pursuant to the
Preferred Subscription Agreement, dated as of May 6, 2003, among Waste Services,
Inc., the Company, KIA and KEP (as amended from time to time, the "PREFERRED
AGREEMENT"), and, for this purpose, including (x) any securities issuable to the
Kelso Entities or to any Affiliate or Associate of either Kelso Entity by the
Company of its Affiliates upon any conversion or exchange of such securities
(including, without limitation,


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pursuant to Section 6.7 of the Preferred Agreement) or any securities issued as
a divided or other distribution with respect to, or in exchange for or in
replacement of such securities and (y) any securities that may be acquired by a
Kelso Entity from any such Affiliate or Associate of such Kelso Entity or any
employee of a Kelso Entity to the extent such securities were issued to such
Person by the Company or its Affiliates (and any securities issuable upon any
conversion or exchange or such securities or any securities issues as a dividend
or other distribution with respect to, or in exchange for or in replacement of
such securities).


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      IN WITNESS WHEREOF, the undersigned have executed this Agreement as of the
date first written above.



                             CAPITAL ENVIRONMENTAL RESOURCE INC.


                             By:   /s/ George Boothe
                                  ---------------------------------------
                                  Name:  George Boothe
                                  Title: Chief Accounting Officer



                             AMERICAN STOCK TRANSFER & TRUST COMPANY


                             By:   /s/ Herbert J. Lemmer
                                  ---------------------------------------
                                  Name:  Herbert J. Lemmer
                                  Title: Vice President