Government mediators on Thursday requested that Northwest Airlines submit their contentious contract negotiation to arbitration.

The suggestion from the National Mediation Board came in response to a request by the Aircraft Mechanics Fraternal Association and Northwest that they be released from mediated talks.

There is no deadline for Northwest and the union to reply to the board. But if the offer is rejected, it could mark the beginning of a 30 day cooling off period for the two parties, after which the mechanics could strike legally, according to the terms of the Railway Labor Act, an analyst said.

"This virtually assures the commencement of a 30 day cooling off period within the next week or so," said JP Morgan analyst Jamie Baker in a research note. "Our guess is July 21, suggesting midnight Friday, August 19, as the date on which a strike can legally occur."

The union on July 5 asked for an end to federally mediated contract talks, citing lack of progress and inflexibility by the airline. Northwest, which is seeking USD$1.1 billion in annual concessions from its work force, has asked the mechanics to provide USD$176 million of that total.

The union has asked its members to authorize a strike. Members have until July 19 to cast their votes.

Neither side has indicated whether they will accept arbitration.

"Northwest Airlines wants to work with AMFA to reach a consensual agreement that provides wage and benefit levels that are fair to employees and that will allow Northwest to stem its unsustainable operating losses," the carrier said in a statement.

The union said on its web site that it is reviewing the request.