Local 100 of the United Labor Unions filed an official complaint against Dallas Cowboys Owner Jerry Jones with the National Labor Relations Board on Tuesday night.
The union claims that Jones violated the National Labor Relations Act.
The complaint says that Jones' threats to "fire" players if they protest during the national anthem at coming NFL games is illegal. The Local 100 Union says the National Labor Relations Act prevents coercing, intimidating or threatening workers for their "concerted activity".
The union says Jones' is attempting to change working conditions and creating a hostile work environment for the players.
Jones said on Sunday that he would bench anyone who shows disrespect to the American flag. That drew a sharp response from the NFL players' union Monday saying the comments by Jones contradicted assurances last week from Commissioner Roger Goodell and New York Giants President John Mara that players could express themselves without retribution.
The Cowboys and Jones kneeled arm-in-arm before the anthem when they played at Arizona two weeks ago, a few days after Trump said at a rally in Alabama that NFL owners should fire any players who disrespect the flag. All of them stood during the anthem, with arms still locked.
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The Local 100 United Labor Union represents workers in Texas, Arkansas and Louisiana.
So far no response from the Dallas Cowboys.