Referee Shannon Eastin is poised to break a long-time barrier in not only the NFL, but professional American sports, when she becomes the first female on-field official in either the NFL or the MLB, the two biggest pro leagues in the U.S.

With the league's officials union locked in a collective bargaining agreement battle with the NFL, the league has taken to hiring non-union officials for the preseason, which started on Sunday night. The league hopes to resolve the labor dispute, the first since 2001, before the beginning of the regular season.

Eastin, according to the Chicago Tribune, has been a high school and small-college ref, but on Thursday, she will be a part of the officiating crew for the Green Bay Packers-San Diego Chargers game on Thursday night.

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