BOSTON (AP) – If Alex Rodriguez doesn’t mind taking a pay cut to play for a contender, why would the baseball players’ union?

The answer is in the major league collective bargaining agreement, which has rules to protect players making considerably less than $25 million a year who might be pressured to sacrifice their rights to save their job.

“It’s a basic feature of collective bargaining that’s to stop the bosses from insisting that one of the workers take less money in order to keep a job,” said Paul Weiler, a Harvard Law School professor who has written a textbook on sports law.

“The difference is, he’s not a nurse making $22,000 a year, he’s making 22 million bucks a year. But it is that basic principle that they want to adhere to.”

A deal that would have sent Rodriguez to Boston for Manny Ramirez hinged upon an agreement in which the Texas Rangers shortstop would renegotiate his $252 million, 10-year contract. Rodriguez offered on Thursday to cut $12 million over the life of the contract in exchange for increased marketing and logo use rights, according to his agent, Scott Boras.

But the players’ association rejected the arrangement, and the proposed trade was declared “dead” by Red Sox president Larry Lucchino on Thursday after commissioner Bud Selig put an end to the talks.

In the NFL, where nearly all contracts aren’t guaranteed, teams frequently cut players – or threaten to – if they don’t renegotiate their deals. But baseball’s labor agreement says that players can only renegotiate deals to add benefits, not give them away.

“One of the key victories baseball players have that football players don’t have is the concept of the guaranteed contract,” University of Illinois law professor Stephen Ross said Thursday. “It’s not uncommon for owners to overpay players. The union and its members feel that it’s very important that the players not be pressured to give back what they’ve been promised.”

The contract Rodriguez signed with Texas in December of 2000 is still the richest in team sports history, and one that was supposed to make him the cornerstone of a contender. But the Rangers have finished last three straight years with him; he wants out, and the team agrees that it has a better chance to build without spending one-fourth of its payroll on one player.

The Rangers and Red Sox worked out a trade to swap the AL MVP for Ramirez, whose $20 million annual salary is second only to Rodriguez’s. Boston wanted Rodriguez to renegotiate his deal first, and he initially agreed to a cut that would cost him $28 million to $30 million, Boras said.

But the players’ association rejected the proposed changes on Wednesday, saying it could only approve a restructuring that moved the money around, not a renegotiation that diminished it.

“It was clear it crossed the line … and by a huge margin,” said Gene Orza, the union’s No. 2 official. “The principal involved is a transcendent one, affecting all of Alex’s fellow players. To his credit, Alex, from the outset, recognized this.”

The basic agreement between baseball’s players and owners is 223 pages long. Right on Page 1, in Article II, is a clause that states, “An individual Player shall be entitled to negotiate … (2) Special Covenants to be included in an individual Uniform Player’s Contract, which actually or potentially provide additional benefits to the player.”

The Red Sox argued that the benefit for Rodriguez is the ability to play for his chosen team – one that was five outs from the World Series last year – instead a perennial loser. He would also have gotten increased marketing rights, not to mention a better chance of winning another MVP award.

Ross said intangibles such as wanting to play for a winner or closer to home aren’t good enough.

“I think, unfortunately, this is an important principle,” said Ross, a Dodgers fan who would like to see the deal go through because of reports that the Red Sox would trade shortstop Nomar Garciaparra to Los Angeles. “The idea that the player will take less money to play on a team the player prefers is just a way to cut the heart out of the added benefit clause.”

Ross said it’s not hard to imagine a team offering to trade a role player making $1 million to a team where he could start – if he cut his salary in half. Many players would jump at the chance, but it would undermine the guaranteed salaries the union fought for.

“If somebody could figure out a way to distinguish A-Rod from my guy, then they’d be in good shape,” Ross said. “From a human point of view … whatever (Rodriguez) is going to make is still so much money. But the principle is the same principle that applies.”