Unionized Hawaiian Airlines pilots said they believe their contract negotiations with the airline are at an impasse and have asked the federal government to release them from mediation, a process that could start the clock for a strike.

In a letter sent to the National Mediation Board on behalf of the pilots, the Air Line Pilots Association requested that the NMB end its mediation efforts and issue a "proffer of arbitration" to both parties.

A rejection of the offer by either side would mark the end of mediation.

"The Association believes that further mediation is not likely to lead to an agreement and that further bargaining, in the absence of a proffer, will be futile," ALPA President John Prater said in a news release.

In a response, Hawaiian Airlines said:

"ALPA's request is nothing more than posturing for negotiations, which continue with the oversight of the National Mediation Board. Hawaiian remains committed to reaching a fair agreement with its pilots union."

Under the federal Railway Labor Act, the pilots must get approval from federal mediators supervising the contract talks and must go through a 30-day "cooling off" period before any strike action can be taken.

Hawaiian, which was founded in 1929, has never had a strike.

The airline and its pilots have been in contract talks for about two years.

ALPA said Hawaiian is making money, expanding routes and buying new planes but is not sharing its success with its employees.

The company said it is not seeking concessions but needs work-rule changes to boost pilots' productivity, which the company said lags that of its competitors.

The company said productivity improvements are necessary for Hawaiian's expansion plans, which include more than $5 billion in new Airbus aircraft and the addition of several new long-haul routes in Asia and North America.

Pilots at Hawaiian earn an average of about $150,000 a year, the company has said.