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UNITED STATES v. LOCKE

Opinion of the Court

proaches taken by the Court in various contexts. We need
not discuss that careful explanation in detail, however. To
explain the full intent of the Rice quotation, it sufﬁces to
quote in full the sentence in question and two sentences pre-
ceding it. The Rice opinion stated: “The question in each
case is what the purpose of Congress was. Congress legis-
lated here in a ﬁeld which the States have traditionally occu-
pied. So we start with the assumption that the historic po-
lice powers of the States were not to be superseded by the
Federal Act unless that was the clear and manifest purpose
of Congress.”

331 U. S., at 230 (citations omitted).

The qualiﬁcation given by the word “so” and by the pre-
ceding sentences in Rice are of considerable consequence.
As Rice indicates, an “assumption” of nonpre-emption is not
triggered when the State regulates in an area where there
has been a history of signiﬁcant federal presence. See also
Jones v. Rath Packing Co., 430 U. S. 519, 525 (1977) (“as-
sumption” is triggered where “the ﬁeld which Congress is
said to have pre-empted has been traditionally occupied by
the States”); Medtronic, Inc. v. Lohr, 518 U. S. 470, 485 (1996)
(citing Rice in case involving medical negligence, a subject
historically regulated by the States).
In Ray, and in the
case before us, Congress has legislated in the ﬁeld from the
earliest days of the Republic, creating an extensive federal
statutory and regulatory scheme.

The state laws now in question bear upon national and
international maritime commerce, and in this area there is
no beginning assumption that concurrent regulation by the
State is a valid exercise of its police powers. Rather, we
must ask whether the local laws in question are consistent
with the federal statutory structure, which has as one of its
objectives a uniformity of regulation for maritime commerce.
No artiﬁcial presumption aids us in determining the scope of
appropriate local regulation under the PWSA, which, as we
discuss below, does preserve, in Title I of that Act, the his-
toric role of the States to regulate local ports and waters