NEW YORK (CNN/Money) - Shares of UAL Corp. resumed trading Thursday afternoon, although the New York Stock Exchange warned it would watch trading of the United Airlines parent closely to see if another suspension in trading and delisting of the stock is warranted.

The airline's request for $1.8 billion in federal loan guarantees was rejected by the Air Transportation Stabilization Board late Wednesday, apparently leaving the airline with little chance to avoid filing for bankruptcy protection.

Shares of UAL (UAL: down $2.08 to $1.04, Research, Estimates) lost about two-thirds of their value from Wednesday's close in the early minutes of trading Thursday afternoon. Shares had lost $1.84, or 59 percent, to $1.28 in consolidated trading on the Pacific Stock Exchange, early Thursday. There was no morning trading on the floor of the NYSE, as the exchange halted trading for its pending news announcement.

The NYSE statement repeated the company's prediction of a bankruptcy filing without federal help, and said it would closely monitor trading in the stock once it started.

"The exchange notes that it may make an appraisal of, and determine on an individual basis, the suitability for continued listing of an issue in light of all pertinent facts whenever it deems such action appropriate, and that the exchange may, at any time, suspend a security if it believes that continued dealings in the security on the NYSE are not advisable," said the statement.