Updated from 12:01 p.m. EDT

United Airlines is expected to file for bankruptcy on Monday according to several published reports, a move that industry analysts and observers had been predicting since the company's bid for federal loan guarantees was rejected last week.

The Wall Street Journal, The New York Times and Reuters were among the news agencies reporting that the airline, a unit of UAL ( UAL), was preparing to seek protection from its creditors. A bankruptcy filing by United would be the largest of all time for an airline and one of the biggest ever in terms of assets.

Union leaders at United were acknowledging over the weekend that the carrier is probably heading for bankruptcy, according to several reports. The statements from union representatives came as the board of UAL met for talks.

Several publications reported that the machinists' union told members that a bankruptcy filing from the airline now appears "unavoidable and imminent." That statement echoed the opinion of several observers who thought bankruptcy became all but certain after the Air Transportation Stabilization Board rejected United's application for $1.8 billion in loan guarantees last week.

Additionally, CEO Glenn Tilton, after meeting with union officials, said on a company hot line that Chapter 11 was becoming "a more likely outcome," the Associated Press reported.

United, though the most prominent carrier in the news of late, hasn't been alone in its struggles. The New York Times reported Saturday that David Bronner, the chief executive of the primary lender to bankrupt US Airways, said he would liquidate the airline if unions refused to provide $200 million in additional wage and benefit concessions.

Bronner, the CEO of the Retirement Systems of Alabama, said he doesn't expect to have to follow through on the threat, and he predicted that cost-cutting talks between the airline and its workers would result in a deal, the Times reported.

Separately, AMR's ( AMR) American Airlines has asked employees to forgo pay increases next year as part of the company's bid to stem short-term financial losses. Company executives have met with union leaders and other employee groups to make their case.

In a press release Friday, AMR said "by forgoing all of the scheduled pay increases, the company will avoid an immediate annual cost increase of $130 million, which will keep American's financial situation from worsening."