An OHL rule change has prompted the National Hockey League Players' association to take action.

The NHLPA has filed an anti-trust lawsuit against the Ontario Hockey League over a rule, adopted in the wake of the Mike Ryn controversy last season, that prohibits clubs from signing 20-year-old players that leave the U.S. college hockey system to play in the OHL.

The NHLPA refused to comment about the case.

In order to prevent other drafted U.S. college hockey players from abusing the system even further, the OHL went back to an old league rule that states players must hold a CHL or USA hockey player as a 19-year-old if they want to play in the league.

Last season, Van Ryn, a highly-regarded defenceman with the University of Michigan, left the school in his bid for unrestricted free agency and moved to Sarnia in 1999 to play for the Sting.

After he completed his one and only season in the OHL, Van Ryn - the New Jersey Devils first-round draft choice, 26th overall - was free to sign with any team in the NHL. He inked a deal with the St. Louis Blues in the summer.

Van Ryn was taking advantage of a ruling change by grievance arbitrator Lawrence Holden. In the decision, he stated that overage players that left a U.S. college hockey program and played one year of major junior hockey could sign with any NHL club as an unrestricted free agent.

U.S. college hockey players remain the property of their NHL team until the draft after the player leaves school. A drafted player in the major junior system is automatically thrown back into the draft if he doesn't sign with the club in two years.

Mike Comrie, Van Ryn's former teammate, pursued a similar course of action and signed with the Kootenay Ice of the Western Hockey League last September. Since the Edmonton Oilers didn't want to lose Comrie, a highly-rated prospect, in the off-season, the team signed him to a lucrative contract that could pay him up to $3 million US a season.