Air Force and UNLV are expected to remain in the Mountain West, sources confirmed to ESPN.

Both schools were incentivized to stay with significant financial packages made possible, in part, by the collective exit fees the conference's five departing members -- Boise State, Colorado State, Fresno State, San Diego State and Utah State -- will be responsible paying for leaving for the Pac-12. Each school is expected to pay roughly $18 million to depart.

UNLV chose to remain in the Mountain West despite overtures from the Pac-12, while Air Force received heavy interest from the American Athletic Conference. With both pledges, the Mountain West stands at seven football-playing members and will need to add two more full members to meet the NCAA minimum criteria (Hawaii is only a partial member).

The decision from UNLV is a blow to the Pac-12, which was optimistic the Rebels would join the five other MWC schools in the new-look conference as it rebuilds from last year's collapse. The Pac-12 is left with seven members and will likely have to turn its attention outside the Mountain West as the rest of the conference's schools -- Hawai'i, New Mexico, Nevada, San Jose State and Wyoming - are expected to sign binding agreements to stay in the conference on Thursday.

This all comes a day after the Pac-12 filed a lawsuit in federal court challenging the legality of a "poaching penalty" included in a football scheduling agreement it signed with the Mountain West Conference in December.

As part of the agreement, the Mountain West included language that requires the Pac-12 to pay a fee of $10 million if a school left the MWC for the Pac-12, with escalators of $500,000 for each additional school. With the five departures, the total the Mountain West feels it should be paid stands at $55 million.

"This action challenges an anticompetitive and unlawful 'Poaching Penalty' that the MWC imposed on the Pac-12 to inhibit competition for member schools in collegiate athletics," the lawsuit says. "The 'Poaching Penalty' saddles the Pac-12 with exorbitant and punitive monetary fees for engaging in competition by accepting MWC member schools into the Pac-12."

On Monday, UNLV and Air Force both reaffirmed their commitment to the Mountain West but softened that stance the same day in the wake of Utah State's decision to leave in a whirlwind day for college realignment that also saw Memphis, Tulane, South Florida and UTSA all pass on offers to join the Pac-12 to remain in the AAC.

The news was first report by the Action Network.