The Major League Baseball Players Association said Saturday it will support Alex Rodriguez if the Yankees withhold a $6-million payment -- negotiated in a 2007 marketing agreement -- for tying Willie Mays with 660 home runs, a feat accomplished by Rodriguez Friday night.

The Yankees reportedly have told Rodriguez they will not make the payment because of Rodriguez's 2014 suspension for alleged use of performance-enhancing drugs.

"The union is prepared to intervene on Alex's behalf," spokesman Greg Bouris said.

Speaking to reporters in Boston, general manager Brian Cashman said it is up to the Yankees to determine whether the payment should be made. "We're going to follow the contract as we follow all contracts," Cashman said. "There is no dispute from our perspective. We're going to honor our responsibilities of the contract . . . I'm going to turn the page and I'll kick it to people above me . . . We have the right but not the obligation to do something. And that's it. It's not 'you do this and you get that.' It's completely different.

"If we choose to pursue something, we'll choose to pursue it. If we choose not to, it's our right not to. And that means in both cases we're honoring the contract."

A source familiar with the agreement said it is the team's option to determine if the homers can be promoted by merchandising or other commercial ventures. Another person who has seen the marketing deal said there is no clause saying Rodriguez would forfeit the payments if he were suspected or penalized for PED use.

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A portion of Rodriguez's contract was broadcast Saturday on YES: "It is the sole discretion of the New York Yankees to determine whether each of these milestones is commercially marketable as the home run chase. The Yankees have the right but not the obligation to determine whether it's a commercially marketable milestone."

If the matter goes to arbitration, former MLB arbitrator George Nicolau told Newsday: "It seems to me the bonus is a bonus. If the contract simply says that if some point that he reaches X, the bonus will be paid, I don't see how the Yankees can get out of it."

With Erik Boland

and David Lennon in Boston