From http://www.moralityinmedia.org/nolc/...nforcement.htm
Selective Enforcement


Selectivity in General - The conscious exercise of some selectivity in law enforcement is not by itself unconstitutional. When attempting to prove unconstitutional selective enforcement it is insufficient merely to show that there is some evidence of selective enforcement.
Burden of Proof - A heavy burden rests on the defendant to show evidence of conscious, discriminatory prosecution.

Equal Protection - A valid statute may be rendered invalid as violative of equal protection if its provisions are selectively enforced. In order to accomplish this the defendant must show that while the law has been consciously and deliberately enforced against him, there is premeditated abstention from enforcing it against others. It is not enough to show that other violators have not been prosecuted. Failure to enforce the law for a certain group does not render charges against another void.

Discriminatory Enforcement - To prove selective enforcement a defendant must also show that the purposeful, intentional decision to concentrate enforcement upon him was based upon an unjustifiable and arbitrary standard such as race or religion, or upon a desire to inhibit First Amendment freedoms.

Rational Relation Test - Enforcement of an ordinance will not be considered unreasonable, arbitrary, capricious, or discriminatory where it reflects a reasonably conceived, legitimate public purpose, or valid law enforcement objective. This is illustrated in Inturri v. Healy and State v. Boivnian where distinctions are drawn between two types of establishments for the purpose of isolating the more provocative for concentrated law enforcement.