Donald Trump has called for an end to the NFL's "massive" tax breaks because of players kneeling during the national anthem.
The US President tweeted: "Why is the NFL getting massive tax breaks while at the same time disrespecting our Anthem, Flag and Country? Change tax law!"
Mr Trump first voiced his anger at the protests, which players say are against racial injustice, but which Mr Trump calls unpatriotic and "disrespectful", last month, soon after the current season started.
On Sunday, he tweeted that he was "proud" of Mike Pence after the Vice-President and his wife walked out of the Indianapolis Colts-San Francisco 49ers game after more than 20 of the 49ers players knelt as the Star-Spangled Banner was played before the match started.
Pence said in a statement: "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.
"At a time when so many Americans are inspiring our nation with their courage, resolve and resilience, now, more than ever, we should rally around our Flag and everything that unites us.
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However, 49ers defensive safety Eric Reid dismissed it as a "stunt" .
Mr Trump has also praised NFL fans who booed Dallas Cowboys players that knelt before the anthem was played at a recent match.
He has insisted that his comments about the demonstrations are "not to do with race" .
The President began the feud by demanding NFL clubs sack players who knelt during the anthem, a demand that NFL chiefs called "divisive".
Initially the complaints backfired, as more, not fewer, players joined the protest.
More than 150 players sat, knelt or raised fists in defiance the following weekend - the biggest display of strength of feeling since the protests began when former 49ers QB Colin Kaepernick knelt during the national anthem to protest perceived racial injustice and police brutality in 2016.
Mr Trump's demands may not come to anything, since the NFL gave up its federal tax-exempt status in 2015.
The tax-exempt status only applied to its office, rather than the clubs, and all NFL income, whether from ticket sales, merchandise, TV rights, sponsorship deals or other means is taxed as normal.