After five years of talks with no new contract, negotiations between US Airways and its flight attendants are headed to federal mediation next week.

The flight attendants, whose negotiations had taken a back seat to contentious contract talks with the carrier's pilots, have recently increased the pressure on US Airways. Since walking out of negotiations in February, flight attendants have picketed airports where US Airways has major operations, including Charlotte.

Flight attendants have also been hinting at the possibility of a strike next year.

Both sides are headed back to the negotiating table on Monday, now under federal supervision by the National Mediation Board.

"That will force the company to have to bargain with us at a reasonable pace, lest they face the possibility of the NMB releasing the flight attendants to seek self-help - strike," said Mike Flores, head of the union master executive council representing about two-thirds of the flight attendants.

US Airways executives declined to comment for this story. A spokeswoman said it wouldn't be prudent to talk publicly so close to the start of mediation.

US Airways has said numerous times that its hubs and domestic routes aren't as lucrative as competitors' larger markets and international routes. To stay afloat, executives say they have to maintain a labor cost advantage to offset that shortfall.

Last year, US Airways reversed years of losses to post a nearly $450 million profit. Though it lost $110 million in the first quarter this year due to higher fuel prices, it wasn't alone - the industry lost over $1 billion.

In February, the flight attendants said US Airways' latest proposal was inadequate and left negotiations. The airline had offered to increase its spending on pay and benefits for the 6,200 flight attendants by $40 million, 10 percent, a year.

The union declined to give a dollar figure for what its seeking.

The dispute has its roots in US Airways' 2005 merger with smaller America West in 2005, which saved the larger carrier from liquidation. As the new airline began to combine its unions and operations, it quickly hit a rough patch.

US Airways managed to combine seven of its nine unions. But pilots from the old "East" (former US Airways) and "West" (former America West) groups were unable to agree on a new seniority list, which determines pay, routes, planes flown and vacation time. The pilots' dispute slid into years of public, labyrinthine legal wrangling, which is still unresolved.

The flight attendants were also unable to reach a merged contract with the airline.

Though they're represented by the same union, the East and West flight attendants still operate under separate, pre-merger contracts. And the crews fly separately - East flight attendants with East pilots, and West flight attendants with West pilots.

Flight attendants from the old US Airways workforce say they're working under a contract in which they gave up huge concessions - up to 40 percent of wages and benefits - negotiated while the airline was in bankruptcy.

The former America West group contends its flight attendants haven't received a raise in nearly a decade, and are paid up to 40 percent less than their counterparts from the East group. Just bringing their pay in line with the East group would take some $44 million a year, said Lisa LeCarre, president of the master executive council representing the West flight attendants in negotiations.

"It's not like (the union) is asking for anything outrageous," she said.

Flores said employees deserve to share the company's prosperity and wouldn't want to enter a contract that could put the company into bankruptcy.

The union hopes that negotiating with a mediator will give the talks a greater sense of urgency and structure. But it's unclear what effect the move to mediated negotiations will have. The pilots union and US Airways have been meeting weekly with a federal mediator since last January, and negotiations remain stalled.

Under the Railway Labor Act, which governs airline unions, workers have to ask the NMB to release them from negotiations before striking, and can't strike until after mediation, possible arbitration and a cooling-off period. The mediation phase, which the flight attendant's case is just entering, can last indefinitely.

The earliest date the flight attendants could ask the NMB to release them to strike is Jan. 1, 2012. A 30-day cooling period would follow if NMB granted permission.