JetBlue Airways has upped its offer to Spirit Airlines. The new offer has been made just a few days ahead of Spirit’s shareholder vote on its merger deal with Frontier Airways.

Frontier had raised its offer on Friday. Ted Christie, the CEO of Spirit Airlines, on Tuesday said that Spirit’s board still found the deal to merge with Frontier Airways to be a superior option to going with JetBlue.

The shareholders of Spirit Airlines are set to vote on Frontier’s cash and stock deal this Thursday. The company had postponed the vote earlier this month to continue the negotiations with both airlines.

The new offer presented by JetBlue has raised the reverse break-up fee from $350 million to $400 million. If regulators don’t accept the deal and include a dividend to Spirit shareholders of $2.50 a share, up from a previous offer of $1.50.