(Reuters) - The National Football League (NFL) will begin testing for human growth hormone (HGH) on Monday, nearly three weeks after the league and its players agreed to a revised drug policy, the NFL’s website said.

Vials of counterfeit human growth hormone seized by the U.S. Customs & Border Protection are seen on display at the agency's offices at John F. Kennedy Airport in New York August 15, 2012. REUTERS/Keith Bedford

NFL Players Association (NFLPA) president Eric Winston outlined the plans in a letter to the players. He also reiterated their right “to challenge any aspect of the science” behind the testing, NFL Media reported.

“Testing for HGH will begin on Monday, October 6th,” Winston wrote. “Each week of the season, five players on eight teams will be tested. No testing will occur on game days.

“We negotiated to ensure that the methodology of testing be conducted in the most professional and safest manner for players.

“Importantly, after three years of negotiating, players won the right to challenge any aspect of the science behind the HGH isoforms test in an appeal of a positive test.”

The revised drug policy between the NFL and the NFLPA was formally announced on Sept. 17, nearly a week after the players’ union agreed to terms for a new policy on a vote by player representatives.

A first violation of the policy, including HGH, will result in a suspension without pay of up to six games depending on the nature of the violation.

A positive test for diuretics or masking agents will result in a two-game ban while a positive test for a steroid, stimulant or HGH will result in a four-game ban.

A second violation of the steroid policy will result in a suspension without pay of 10 games while a third violation will result in banishment for a minimum of two years.

Players who test positive for banned stimulants in the offseason no longer will be suspended but will be referred to the substance abuse program. Players who test positive for stimulants during the season will continue to be banned without pay for four games.

Appeals of positive performance enhancing drug tests will be heard by third-party arbitrators jointly selected by the NFL and the union.

The NFL had struggled for years to reach an agreement with the union over HGH testing and finally did so more than a year after Major League Baseball started testing, and long after many international sports.

The International Olympic Committee first tested athletes for HGH at the 2004 Athens Olympics.

The National Basketball Association and National Hockey League, North American’s two other major sports leagues, do not tests for HGH but both have said they are considering them.