By Greg Roumeliotis and Anirban Sen

NEW YORK (Reuters) -Frontier Group Holdings Inc has agreed to supply a break-up price in a bid to safe its $2.9 billion acquisition of Spirit Airways (NYSE:) Inc, folks aware of the matter mentioned on Thursday.

The sweetening of the phrases comes after proxy advisory agency Institutional Shareholder Providers Inc (ISS) urged Spirit shareholders to vote in opposition to the take care of Frontier, partly as a result of Spirit failed to barter a break-up price ought to U.S. antitrust regulators shoot down their deal.

JetBlue Airways (NASDAQ:) Corp is attempting to gatecrash the take care of a hostile $3.3 billion supply for Spirit that the latter has rejected, arguing regulators is not going to greenlight it until JetBlue makes extra concessions.

Frontier and Spirit might announce a revised deal that they hope will win assist from Spirit shareholders as early as Thursday, the sources mentioned, requesting anonymity as a result of the matter is confidential. The scale of the break-up price couldn’t be realized.

Spirit and Frontier didn’t instantly reply to requests for remark.