PITTSBURGH – No. 2 draft pick Pedro Alvarez refused to sign his contract with the Pittsburgh Pirates, and the players' association filed a grievance Wednesday claiming the Aug. 15 deadline was unilaterally extended by Major League Baseball without the union's permission.

The Pirates announced early on Aug. 16 that Alvarez, a power-hitting third baseman from Vanderbilt, agreed to a minor league contract with a $6 million signing bonus. The Pirates said his agent, Scott Boras, told the team Alvarez would not report unless the deal was renegotiated. Boras claimed the agreement was reached after the midnight deadline for draft picks to sign on Aug. 15.

Alvarez was placed on baseball's restricted list.

“Regrettably, we are not surprised that Mr. Boras would attempt to raise a meritless legal claim in an effort to compel us to renegotiate Pedro's contract to one more of his liking,” Pirates president Frank Coonelly said in a statement, “We are, however, disappointed that Pedro would allow his agent to pursue this claim on his behalf. Pedro showed tremendous fortitude and independent thinking when he agreed to his contract on Aug. 15.”

Michael Weiner, the union's general counsel, said the extension of the deadline “was done without notice to or consultation with the players' association, despite a firm deadline having been established through collective bargaining.” He said the grievance was not filed on behalf of any particular player, and no decision had been made whether to seek to void the deals. The union and MLB hope to schedule a hearing by Sept. 10.

“It is the union's obligation, on behalf of all players, to defend the integrity of its collectively bargained agreements,” he said.

Coonelly said the agreement between the Kansas City Royals and No. 3 draft pick Eric Hosmer was submitted to MLB after Alvarez's deal.

“Mr. Boras is apparently satisfied with the $6 million bonus that he secured for Mr. Hosmer and has not challenged the validity of that contract,” Coonelly said. “Mr. Boras has been informed that if he pursues a claim that our contract with Pedro was not timely, he puts Eric Hosmer's contract with Kansas City in jeopardy.”

Rob Manfred, baseball's executive vice president of labor relations, called the grievance “entirely without merit.”

“The deadline was extended to accept minor league contracts voluntarily entered into by the clubs and the players with the help of their agents,” he said. “It is settled law that the arbitration panel has no authority to disturb such minor league contracts.”

Boras declined comment, saying Weiner would speak for him.

While Alvarez and Hosmer agreed to $6 million signing bonuses, No. 5 pick Buster Posey got an agreement with a $6.2 million signing bonus from the San Francisco Giants.

Royals general manager Dayton Moore was surprised to see Hosmer's contract brought up.

“We agreed in the appropriate time frame and the terms were submitted in a timely matter,” Moore said. “Eric Hosmer is completely satisfied with the terms of his contract and is completely satisfied with being part of this organization.”

The Pirates are determined, Coonelly said, to not let the contract impasse affect their relationship with Alvarez.

“We continue to believe that in Pedro Alvarez, the person and the baseball player, and remain excited to add Pedro to our system,” Coonelly said. “We will sit down with Pedro as soon as Mr. Boras' claim is rejected to chart a new and more productive start to Pedro's career with the Pittsburgh Pirates.”

AP Baseball Writer Ronald Blum in New York contributed to this report.