A group representing thousands of America's veterans says the NFL "censored" an ad the group wanted to run in the programs sold at next month's Super Bowl.

The ad targeted football players for protesting during the national anthem.

AMVETS National Commander Marion Polk tweeted Monday night that the group "will not tolerate" the NFL's censorship after the group says the football organization refused to print an ad urging players to "#PleaseStand" during the Feb. 4 championship game between the New England Patriots and Philadelphia Eagles.

The ad, which can be viewed on the group's website, depicts three service members holding the American flag next to the text "#PleaseStand." The group planned for the ad to be printed in the programs passed out to fans attending the game.

".@AMVETSHQ will NOT tolerate the @NFL refusing #Veteran right to free speech. We fought for it!" Polk said Monday.

In an open letter to NFL Commissioner Roger Goodell dated Monday, Polk blasted the league for using soldiers and military vehicles as "props" during games while refusing to air the ad from AMVETS.

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"Mr. Goodell, veterans are good for more than just military flyovers, photo opportunities during halftime, or props to sell camouflage-style NFL apparel," Polk wrote.

"Our ad is neither a demand nor judgment upon those who choose to kneel during our National Anthem," Polk added. "It's a simple, polite request that represents the sentiment of our membership, particularly those whose missing or paralyzed limbs preclude standing."

Founded in 1944, AMVETS is the largest and oldest veterans' group in the country, representing 250,000 active members, according to the group's website.

The NFL has been embroiled in controversy for months over players' protests of police brutality and racism during the national anthem, started by former San Francisco 49ers quarterback Colin Kaepernick.

In September, President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE entered the fray and suggested that NFL team owners should fire players who kneel during the anthem, a suggestion that sparked new waves of protests from dozens of players across the league.

In October, Vice President Pence left an NFL game in Indianapolis after players knelt during the national anthem.

"I left today's Colts game because President Trump and I will not dignify any event that disrespects our soldiers, our Flag, or our National Anthem," Pence said at the time in a statement.

Pence added he doesn't think it's "too much to ask NFL players to respect the Flag and our National Anthem."