NEW YORK (CNN/Money) - The International Association of Machinists said Friday the resignation of Treasury Secretary Paul O'Neill should resurrect the rejected application of United Airlines for $1.8 billion in federal loan guarantees.

The three-member Air Transportation Stabilization Board voted 2-1 to reject the loan guarantee application Wednesday afternoon, pushing the world's No. 2 airline to the brink of filing for bankruptcy court protection.

Peter Fisher, the Treasury Department representative on the panel, joined Federal Reserve Governor Edward Gramlich to vote no on United's application, saying the carrier's business plan was not realistic. Kirk Van Tine, the Transportation Department's representative, voted to give United until Monday to present additional information.

"The decision by O'Neill's designee to withhold critical financial assistance to United Airlines must not be allowed to stand,' said a statement from IAM President R. Thomas Buffenbarger. "Common sense demands an immediate review of the outrageous decision by the ATSB to push a great American company to the very brink of bankruptcy."

The IAM represents about 37,000 United Airlines ground workers, including mechanics, baggage handlers and customer service representatives.

Neither a Treasury Department spokeswoman who speaks for the ATSB nor a United spokesman had any comment on the IAM statement.

Shares of UAL (UAL: down $0.07 to $0.93, Research, Estimates) lost more than 15 percent Friday after losing more than two-thirds of their value Thursday following the ATSB vote.