The head of the American Legion said Monday that NFL players and other professional athletes who do not stand for the national anthem are "misguided and ungrateful."

The group, which includes 2 million veterans, along with the Veterans of Foreign Wars service organization, dived into the growing controversy surrounding President Trump's criticism of professional athletes who have begun kneeling as the song is played at games in quiet protest of racial injustice.

"There are many ways to protest, but the national anthem should be our moment to stand together as one United States of America," Denise Rohan, the commander of the American Legion, said in a statement.

Players across the NFL protested during the "Star-Spangled Banner" at games on Sunday. Alejandro Villanueva, a Pittsburgh Steelers player, stood on the field alone as all of his teammates stayed in the locker room.

Rohan, who is the Legion's first female national commander, said the veterans organization "salutes" Villanueva as well as fans and drivers at a NASCAR race Sunday for supporting the anthem.

"There are many ways to protest but the national anthem should be our moment to stand together as one United States of America," she said. "Having a right to do something does not make it the right thing to do."

The VFW, which claims 1.7 million veteran members, also slammed the practice that was first popularized by Colin Kaepernick, a professional football quarterback not currently signed to a team.

"There is a time and place for civil debate, and wearing team jerseys and using sporting events to disrespect our country doesn't wash with millions of military veterans who have and continue to wear real uniforms on real battlefields around the globe," said Keith Harman, the VFW national commander.

On Friday night, Trump said the NFL should fire players who kneel during the anthem and fired off another tweet Monday morning following Sunday's games, saying fans feel the same way.

"Many people booed the players who kneeled yesterday (which was a small percentage of total). These are fans who demand respect for our Flag!" he tweeted.