United Airlines (UAL) mechanics and cleaning crews, in a vote announced late on Tuesday, emphatically rejected the company's contract proposal, setting the stage for a possible strike next week at the financially troubled No. 2 U.S. airline.

The 13,000 union members, represented by International Association of Machinists and Aerospace Workers District Lodge 141-M, voted the contract down by 68 percent and, in a separate vote, authorized a strike by 86 percent.

The rejected contract offer included immediate pay raises of as much as 37 percent, but required them to give back some of those wages soon to aid the struggling carrier's recovery effort.

A walkout could begin as soon as Feb. 20 unless a last-minute settlement or congressional action blocks it.

The White House said Wednesday it would monitor talks between United's management and mechanics and cleaning crews. President Bush has warned he does not want to see airline workers on strike during hard economic times, and has already used his powers to head off other possible walkouts.

"The parties have indicated that they are going to continue to meet and work in good faith to get an agreement, and the White House will monitor those talks and see where they go, but that is where the action is now," said White House spokesman Ari Fleischer.

The union and airline have been in direct and federally mediated negotiations since December 1999. The contract became open in July 2000.

Top machinists at other major airlines, including AMR Corp.'s (AMR.N) American Airlines and Northwest Airlines (NWAC.O), are paid an hourly wage about 30 percent above the rate at United Airlines.

The airline's offer was recommended by an emergency board appointed by President Bush in December.

Under the offer, a top United mechanic paid $25.60 an hour would have received a raise to $35.14 immediately and to $37.54 by mid-2004, surpassing the $34 received by American Airlines mechanics.

Several union lodges had recommended a "no" vote because of looming wage givebacks and the fact that employees wouldn't receive retroactive pay for work dating to July 2000 until eight quarterly payments beginning in April 2003.

United has said employee concessions are necessary if it is to recover from last year's record-setting $2.1 billion loss. The airline laid off 20,000 employees and slashed its schedule last fall.

Reuters and the Associated Press contributed to this report.