Two United Continental Holdings Inc. shareholders, seeking a board shakeup as the top executive returns from a heart transplant, will nominate a director slate led by a turnaround artist from a predecessor airline. Hedge funds Altimeter Capital Management LP and PAR Capital Management Inc. said Tuesday they’re backing six new board members led by Gordon Bethune, the former chief executive officer of Continental Airlines, which merged with United in 2010. The announcement came a day after United named three independent directors of its own—and just as CEO Oscar Munoz is set to return from medical leave. The moves set up a boardroom brawl at an airline that’s trying to mend labor relations and improve operational performance as it struggles with the aftermath of its 2010 merger with Continental. United has a history of lagging Delta Air Lines Inc. and American Airlines Group Inc. in on-time arrivals and profit margins despite some recent improvements. “As long-term United stockholders, we have been greatly disappointed with United’s poor performance and bad decisions over the last several years,” Altimeter CEO Brad Gerstner said in a statement. “Yesterday’s last-ditch effort –- adding just three people to its now 15-person board –- is a cynical attempt to preserve power by this entrenched board.” Friday is the deadline to nominate directors. There is still a chance the two sides could reach an agreement, Bethune said. United fell 2.8 percent to $56.01 at 10:41 a.m. in New York. United Response United said the investor group refused to make its nominees available to be interviewed, a necessary step before the airline would recommend any of the candidates to shareholders. The airline is disappointed that “PAR and Altimeter have unilaterally taken this hostile action with no concern that a proxy fight could distract the Company from executing on Oscar’s strategic plan,” Chairman Henry Meyer III said in a statement. The activist-backed slate isn’t specifically targeting United’s CEO, said Bethune, who recruited Munoz to Continental’s board more than a decade ago. “I won’t stay for more than 2 years. I really am getting too old to do this,” Bethune, 74, said in an interview. “But I want to help the people who are my friends, who are the employees.” Chairman Role Bethune said he was one of the first people Munoz called after being named CEO in September and cut short a vacation in Croatia to fly to Chicago to provide counsel on how best to tackle entrenched labor and operations shortfalls. The former Continental CEO said his intent isn’t to spawn further chaos at United, which is still recovering from the merger integration, or to undermine Munoz in his efforts to repair operations and morale. Rather, Bethune said he was asked by PAR and Altimeter to bolster those efforts with a board role, but talks with United to bring him in as chairman broke down. “You can’t be effective as one guy unless you come in as chairman,” Bethune said. “I would not go, nor think about going in just as a board member. I don’t need a job.” PAR was part of group that helped Doug Parker engineer America West’s takeover of the larger U.S. Airways in 2005. The fund’s 14.1 million shares of United, 3.9 percent of the carrier’s stock as of Feb. 10, is PAR’s largest holding. Altimeter’s stake was 3.2 percent as of Jan. 19, according to data compiled by Bloomberg.