The Federal Communications Commission (FCC) appealed to the US Supreme Court in 2008 to force the TV network to pay a $550,000 (£345,270) fine.
The FCC said it was disappointed by Wednesday's ruling. CBS said it was grateful for the decision.
The 3rd US Circuit Court of Appeals in Philadelphia said that in imposing the fine, the FCC "improperly imposed a penalty on CBS for violating a previously unannounced policy".
Full piece BBC