WASHINGTON (AP) — Northwestern University is asking the National Labor Relations Board to overturn a regional director's ruling that the school's football players are employees under federal law and thus entitled to unionize.

The university filed a formal appeal board Wednesday.

Northwestern says that it had presented "overwhelming evidence" that its athletic program "is fully integrated with its academic mission, and that it treats its athletes as students first."

The players are set to vote by secret ballot April 25 on whether to form a union.

Former Northwestern quarterback Kain Colter and Ramogi Huma of the College Athletes Players Association met in Washington with members of Congress earlier this month to press their case for unionization.