On Thursday, the court issued a ruling quashing an arbitrator's decision in June that Williams's contract with the Hamilton Tiger-Cats was binding even though the club violated the CFL's collective bargaining agreement with the CFLPA.
"It is the position of the CFLPA that Chris Williams is now a free agent and able to sign a contract in the NFL or another CFL club," the union said in a statement.
Dan Vertlieb, Williams' agent, didn't immediately respond to an email request for comment from The Canadian Press.
Williams, 25, the CFL's top special-teams player last season, went to arbitration asking to be released from the final year of his contract with Hamilton to reportedly pursue NFL offers.
In June, arbitrator E.E. Palmer found the Ticats violated the CBA by negotiating with an unregistered agent but said the penalty was a fine and not the termination of the contract.
However, the Ticats weren't fined because the CFLPA did not request one be imposed.
Palmer also found Hamilton had picked up the option on Williams's contract last October in accordance to the CBA but didn't use the exact language surrounding the renewal as laid out in the agreement.
But he also ruled that wasn't enough to null the agreement.
Both the Ticats and CFL said they'll appeal Thursday's ruling.