Washington, Jul 21 (IANS): US President Donald Trump on Saturday asked the National Football League to suspend players who kneel during the national anthem this coming season.

Trump questioned the players' contracts and proposed two tiers of punishment.

"The NFL National Anthem Debate is alive and well again - can't believe it! Isn't it in contract that players must stand at attention, hand on heart?" he tweeted.

"The $40,000,000 Commissioner must now make a stand. First time kneeling, out for game. Second time kneeling, out for season/no pay!" he added.

Trump has in the past rigorously criticized NFL athletes who kneel during the national anthem before games to protest police brutality against African-Americans in the US, Efe reported.

In addition to kneeling, others choose to cross their arms -- a silent protest that began during the 2016 season.

The NFL approved in May a new regulation to fine teams whose players kneel during the national anthem, although they are allowed to remain in the dressing rooms until the start of the game.

Trump celebrated that decision and said athletes who do not stand up during the anthem "probably should not be in the country".

The President's petition comes after Tennessee Titans' defensive end Jurrell Casey said on Wednesday he plans to protest during the US national anthem this coming season, which starts in three weeks.