20880302_ferences__July_2014_FIDE_Laws___FIDE_rule
[0] 5. [USCF rule] The penalty for an illegal move is to add two minutes to the opponent's clock. There is no limit on the number of illegal moves a player may make in a game. [FIDE rule] 
The penalty for the first illegal move is to add two minutes to the opponent's time. A second illegal move results in loss of the game.
The United States Chess Federation - USCF - FIDE Rule Differences (July 2014 FIDE Laws)
FIDE rule