Two hedge funds have engaged outside PR counsel as they mount a proxy challenge to airline giant United Continental Holdings' board.

unitedAltimeter Capital Management and PAR Capital Management, minority shareholders of UCH, are running a six-member slate of directors led by ex-Continental CEO Gordon Bethune.

The firm are working with New York-based financial PR firm ASC Advisors and proxy solicitation firm Okapi Partners in the fight.

ASC is led by Abernathy MacGregor vet Steve Bruce and former head of communications for Elliott Management Scott Tagliarino. Tagliarino and director Taylor Ingraham, formerly of Joele Frank, are advising the funds.

The funds said they tried to work with the United board but claimed the company "hurriedly" added three directors to its board on March 7 in expanding it to 15 directors. Altimeter CEO Brad Gerstner said as long-term shareholders "we have been greatly disappointed with United's poor performance and bad decisions over the last several years."

United Continental, in a statement, said it is "deeply disappointed" in the proxy contest, claiming it offered a willingness to make "meaningful changes to our board" in talks with the hedge funds. "PAR and Altimeter have unilaterally taken this hostile action with no concern that a proxy fight could distract the Company from executing on [CEO] Oscar [Munoz]'s strategic plan," the company said.

Munoz returned to work this month as CEO after a heart transplant.