Thu May 3, 2012 9:14pm EDT (Reuters) - Three labor unions at American Airlines are appealing directly to the company's board of directors to support a merger with rival carrier US Airways Group (LCC.N), a step that managers at carrier's parent, AMR Corp (AAMRQ.PK), have so far resisted. In a letter addressed to the board and signed by leaders of unions representing 55,000 flight attendants, pilots and ground workers, the unions say a merger plan offered by US Airways will save jobs, boost revenue and shore up the combined network of the two airlines. AMR, based in Fort Worth, Texas, which filed for Chapter 11 bankruptcy in November citing a need to cut labor costs, has said it is committed to emerging from Chapter 11 as a stand-alone company. US Airways declined comment on labor's outreach to American's board. American said the maneuver changes nothing, that the airline will continue on its restructuring path that includes a proposal to abrogate union contracts. It should be easy for anyone to understand the agendas of other interested parties and their sense of urgency to advance them, and their actions continue to demonstrate that. We don't need to address them again," spokesman Bruce Hicks said in an emailed statement. Hicks noted that American executives have said the carrier's restructuring will be disciplined and dictated by facts, including whether the company chooses consolidation down the road. "This is the charge of the board of directors and the leadership team to be done in close collaboration with the creditors committee," Hicks said. US Airways, formed from a 2005 merger with America West Airlines, still has not integrated its pilots' and flight attendants' work groups. Separately, American is challenging a decision by federal mediators to allow a union representation election for about 10,000 non-union airport agents and other passenger service workers. The airline said in a suit this week in Texas that the National Mediation Board (NMB) applied an outdated standard for gauging the level of worker support needed to hold a union election. The NMB could not immediately be reached for comment. The suit is not part of American's bankruptcy case. Reporting by Kyle Peterson; Editing by Steve Orlofsky and Eric Meijer