NEW YORK -- Major league baseball umpires threatened more legal action against owners over management's insistence that union representatives leave dressing rooms 30 minutes before games begin.

Union lawyer Larry Gibson said Thursday that owners violated the umpires' labor contract by setting the time limit and by threatening to remove union representatives from ballparks and to revoke their credentials if they violate the time limit.

He said owners also violated umpires' rights by prohibiting non-lawyers associated with the union from entering the dressing rooms without advance permission from management.

"Your threats are highly offensive and very unprofessional,'' Gibson said in a three-page letter to Rob Manfred, baseball's executive vice president for labor relations.

"In my 35 years of law practice, you are the only lawyer to have ever threatened me physically,'' Gibson said.

Umpires and owners resumed their fighting last week over Questec, a system that is being used to track ball-and-strike calls by plate umpires. Umpires say the machine doesn't accurately track pitches, and claim owners are using it as an evaluation tool in violation of the labor contract.

Owners sued in federal court last Thursday in an attempt to discipline union head John Hirschbeck, and umpires filed a grievance the following day that accused management of violating their labor contract by refusing to provide information on the controversial system.

Manfred said owners have acted within their rights and had a different view of his Wednesday conversation with Gibson.

"I told him if he could not comply with the conditions under which his credential was issued, his credential would be revoked and he would be asked to leave that stadium,'' Manfred said. "If he considers that violence, that's OK. He is a guest in the facility. I consider it enforcing the rules.''

Gibson, a lawyer for the World Umpires Association, said time limits had not been enforced until now.

"The fact that he's violated the rules previously and we did not catch him is not of any relevance,'' Manfred said.

On Sunday, umpires demanded that Questec Inc. remove a reference on its Web site that says umps support the system. Questec has not removed the reference and has not returned telephone calls seeking comment.