The future of testing for human growth hormone is shaping up to be a contentious issue in negotiations between the NFL and the players’ union, with the league supporting blood-based testing and the union less convinced about its validity.

Kevin Mawae, the president of the NFL Players Association, told The Associated Press on Sunday that the union is aware of developing tests, one of which is a blood test that could detect HGH for up to 14 days. But he said the union believes the test that is currently available, which has only about a 48-hour window of detection, “is not completely reliable.”

“The testing of HGH is a CBA (collective bargaining agreement) issue that has been discussed on a number of different occasions,” Mawae said in an e-mail to AP. “The PA and the players of the NFL will always be in favor of fair and competitive play without the use of performance-enhancing drugs.”

The current collective bargaining agreement expires in March, which could lead to a work stoppage during the 2011 season. While the key issues are expected to revolve around finances, the future of the salary cap and free agency, there are signs that the future of drug testing will be an issue.

Over the past several months, the league has become a more vocal supporter of blood-based testing, saying the current blood test — widely available since 2008, but not used by the NFL — is reliable, while the test that’s being developed could add another way to catch HGH users.

“I don’t necessarily subscribe to the view that the short detection window by itself renders the (current) test inadequate,” Adolpho Birch, who oversees the NFL’s drug policy, told the AP in an interview last week. “It does provide a deterrent effect. A longer window is helpful and will do a lot to provide better detection. I don’t know if it’s a game-changer, per se, but it is important.”