(a) Unless a person is engaging in any activity which is expressive of rights guaranteed under the Constitution of the United States or the Constitution of this state, a person is guilty of obstructing free passage when, after being warned by a law enforcement officer not to do so, he (1) stands, sits or lies in or upon any public street, curb, crosswalk, walkway area, mall or the portion of private property utilized for public use, so as to obstruct unreasonably the free passage of pedestrians thereon, or (2) obstructs unreasonably or prevents free access to the entrance to any building open to the public.
(b) Obstructing free passage is a class C misdemeanor.