NFL team owners will consider requiring players to stand for the U.S. national anthem after President Donald Trump on Tuesday stepped up his criticism of silent player protests against racial injustice by targeting the league on taxes.

Trump, a Republican, escalated his feud with the National Football League in a Twitter post asking if the league should get tax breaks while players kneel in protest when the "Star-Spangled Banner" is played at the start of each game.

The world's top-grossing sports league gave up its controversial tax-free status two years ago. Its owners are preparing to address the anthem issue at their fall meeting in New York Oct. 17-18, NFL chief spokesman Joe Lockhart told reporters on a conference call on Tuesday.