Citing concerns over federal regulators squelching the sale, South Florida based Spirit Airlines turned down a buyout offer from Jet Blue on Monday.

Spirit’s board of directors will continue to pursue Denver based Frontier Airlines’ February purchase offer of $2.9 billion in cash and stock.

Competitor Jet Blue offered $3.6 billion for the low cost carrier last month, but Spirit leaders determined that federal regulators would likely not allow deal to go through due to anti-trust concerns.

No timeline for the proposed merger has been announced and it is not clear if the airlines will continue to operate under separate brand names.