JetBlue Airways tried to sweeten its offer to acquire Spirit Airlines Inc. on Monday, according to Reuters, enhancing its offer as Spirit stockholders prepare to meet on Friday to discuss a proposal from Frontier.

Both JetBlue and Frontier are racing to acquire Spirit to boost their stronghold on the low-cost airline market.

JetBlue’s new proposal offers Spirit stockholders a greater cash value and more regulatory protections.

The offer includes a reverse break-up fee of $350 million if the sale is not completed due to antitrust concerns, which is $150 million more than JetBlue’s original proposal.

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“We know what it takes to get this deal done. We need the Spirit board to seriously consider our offer,” JetBlue executive Robin Hayes said.

JetBlue also offered to prepay $1.50 per share of the reverse break-up fee in cash. This would be paid as a cash dividend to all Spirit stockholders after the vote to approve the acquisition.

Under the new terms, JetBlue would pay each shareholder $31.50 per share, with $30 coming at closing and $1.50 from the revised break-up fee. This pushes the overall offer to a total of $3.4 billion.

Savanthi Syth, airline analyst at Raymond James, said the revised offer is likely to “appease” Spirit shareholders who have antitrust concerns about a deal with JetBlue.

Spirit shareholders will vote on the Frontier offer on Friday, initially valued at $2.9 billion. Spirit will evaluate JetBlue’s new offer in due time, and leadership told shareholders not to take any action until that evaluation is complete, according to Reuters.

Proxy advisory firm Glass Lewis recommended last week that Spirit investors approve the proposed merger by the Frontier Group, Reuters reported. Fellow proxy firm, Institutional Shareholder Services Inc, advised against the deal.

Both firms will likely issue new recommendations in light of JetBlue’s latest offer.