MINNEAPOLIS — The head of the players’ association thinks the Houston Astros have manipulated baseball’s rules in an attempt to save money in their negotiations with top draft picks Brady Aiken and Jacob Nix.

Aiken, a left-handed pitcher from San Diego, was selected by Houston with the top pick in last month’s amateur draft. Nix, a right-hander from Los Alamitos, California, was taken by the Astros in the fifth round with the 136th pick. Both have committed to UCLA if they don’t sign with Houston.

Aiken originally was offered a deal with a $6.5 million signing bonus by the Astros, a person familiar with the negotiations said, speaking on condition of anonymity because no statements were authorized.

But the Astros expressed a concern over Aiken’s elbow ligament and are now offering $3,168,840, the person said, an amount 40 percent of the slot’s value of $7,922,100. That is the minimum the club must offer to receive an extra top draft pick next year if it fails to sign him by Friday’s 5 p.m. EDT deadline.

Nix was offered a $1.5 million bonus, the person said, but the Astros won’t finalize his deal unless they reach an agreement with Aiken. If they don’t sign Aiken, the Astros would lose the entire slot value from their signing pool.

Both players are being advised by Casey Close.

“It is disappointing on any number of levels to think that what has happened in that situation, what has happened with respect with integrity of the draft process in general,” union head Tony Clark told the Baseball Writers’ Association of America on Tuesday. “Our hope here going forward is that what we think has happened didn’t happen. But you can rest assured that the manipulation that we think happened in this case is going to lead us to have some conversations that are going to make sure that players receive the support that they deserve.”

Speaking earlier to the BBWAA, Major League Baseball Executive Vice President Dan Halem defended the team and said “we fully support the Astros.”

“We believe that they have conducted themselves appropriately,” Halem added. “Given that there are still a few days until the signing deadline, we’re not going to say anything else at this time and, hopefully, all the parties will be able to resolve this without our assistance.”

Astros general manager Jeff Luhnow said in a statement “throughout this process, we have been in touch with MLB to ensure that we are adhering to the rules at every point and we are confident that this has been the case.”