I found the following in Title 18 of the US code:
Sec. 1752. Temporary residences and offices of the President and others
(a) It shall be unlawful for any person or group of persons -
(1) willfully and knowingly to enter or remain in
(i) any building or grounds designated by the Secretary of
the Treasury as temporary residences of the President or other
person protected by the Secret Service or as temporary offices
of the President and his staff or of any other person protected
by the Secret Service, or
(ii) any posted, cordoned off, or otherwise restricted area
of a building or grounds where the President or other person
protected by the Secret Service is or will be temporarily
visiting,
in violation of the regulations governing ingress or egress
thereto:
(2) with intent to impede or disrupt the orderly conduct of
Government business or official functions, to engage in
disorderly or disruptive conduct in, or within such proximity to,
any building or grounds designated in paragraph (1) when, or so
that, such conduct, in fact, impedes or disrupts the orderly
conduct of Government business or official functions;
(3) willfully and knowingly to obstruct or impede ingress or
egress to or from any building, grounds, or area designated or
enumerated in paragraph (1); or
(4) willfully and knowingly to engage in any act of physical
violence against any person or property in any building, grounds,
or area designated or enumerated in paragraph (1).
(b) Violation of this section, and attempts or conspiracies to commit such violations, shall be punishable by a fine under this title or imprisonment not exceeding six months, or both.
(c) Violation of this section, and attempts or conspiracies to commit such violations, shall be prosecuted by the United States attorney in the Federal district court having jurisdiction of the place where the offense occurred.
(d) The Secretary of the Treasury is authorized -
(1) to designate by regulations the buildings and grounds which
constitute the temporary residences of the President or other
person protected by the Secret Service and the temporary offices
of the President and his staff or of any other person protected
by the Secret Service, and
(2) to prescribe regulations governing ingress or egress to
such buildings and grounds and to posted, cordoned off, or
otherwise restricted areas where the President or other person
protected by the Secret Service is or will be temporarily
visiting.
(e) None of the laws of the United States or of the several States and the District of Columbia shall be superseded by this section.
(f) As used in this section, the term ''other person protected by the Secret Service'' means any person whom the United States Secret Service is authorized to protect under section 3056 of this title when such person has not declined such protection.
Also title 18, section 3056, part d reads:
(d) Whoever knowingly and willfully obstructs, resists, or interferes with a Federal law enforcement agent engaged in the performance of the protective functions authorized by this section or by section 1752 of this title shall be fined not more that $1,000 or imprisoned not more than one year, or both.
Usual disclaimer, I AM NOT A LAWYER. Section E in the first part is interesting in reguards to what you asked about.
Jason
[This message has been edited by Jason Kitta (edited July 23, 1999).]