Natural gas producer Ultra Petroleum Corp. (NYSE: UPL) said its auditors raised doubts about its ability to stay in business and that it may have to seek bankruptcy protection in the U.S. or Canada.

The company, reeling from a prolonged slump in commodity prices, said on Feb. 18 that it was considering strategic alternatives and that it had engaged Kirkland & Ellis LLP as legal adviser and Rothschild and Petrie Partners as financial advisers.

Ultra Petroleum said in a regulatory filing on Feb. 29 that it expects to default on a credit agreement on March 15.

The company said it would file for bankruptcy protection if it failed to make debt payments, restructure debt or secure additional capital.

Ultra Petroleum had $3.76 billion in total outstanding debt principal as of Feb. 29.

The company had $1.46 billion due between March 2016 and October 2025 and $630 million due in October 2016.

Ultra Petroleum had a market capitalization of $53.6 million as of Feb. 26's close.

The company's shares were up 5.8 percent at 37 cents in mid-afternoon trading.