(Reuters) - Peabody Energy Corp BTU.N, the largest U.S. coal producer, may have to seek bankruptcy protection, the company said in a regulatory filing on Wednesday, citing poor economies in countries that import coal and other factors battering the coal industry.

Its shares fell 46 percent to $2.16.

Falling demand for coal, tougher environmental controls and cheaper natural gas have pushed several big coal miners, including Arch Coal Inc ACIIQ.PK, into bankruptcy in the past year.

Peabody, which flagged the possibility of bankruptcy under the "risk factors" section of a filing with the U.S. Securities and Exchange Commission, said it had decided to skip $71.1 million in interest payments, kicking off a 30-day grace period. (1.usa.gov/22jEJnJ)

The company, said there was “substantial doubt” about its ability to continue as a going concern. It cited stagnating economic growth in major coal importers and the potential for additional regulatory requirements imposed on producers.

Coal prices TRAPI2Yc1, which hit historic highs above $200 per tonne in 2008, now trade at around $40 a tonne. Goldman Sachs Group has said coal would never gain enough traction to lift it out of its slump.

The U.S. Energy Information Administration on Wednesday forecast that this year will be the first year that natural gas fired generation exceeds coal generation on an annual basis. About a third of U.S. electricity comes from natural gas, versus 32 percent from coal and 19 percent from nuclear. As recently as 2000, coal accounted for about half.

St. Louis-based Peabody, which employed 7,600 people on Dec. 31, said it was also looking into other sources of capital to support its needs for cash and keep it in compliance with creditors. Bond exchanges, cost cuts and waivers to its credit agreements are some of its options, the company said.

Peabody owns interest in 26 mines in the United States and Australia, with about three-quarters of its output going to U.S. electricity generators, according to its filing. It has trading and business offices in Australia, China, and India, among others.

China, where coal imports have slowed to support domestic producers, represented 7.1 percent of total Peabody sales last year.

On March 11, Peabody reported $900 million of cash and cash equivalents. It had reported $261.3 million in cash and cash equivalents at Dec. 31, and then, in February, borrowed the maximum amount available under its revolving credit line, about $945 million.

The company said in a statement its auditors have concluded its current financial path may not be sustainable and “may result in an acceleration of our debt obligations.”

Peabody had total debt of $6.3 billion at the end of 2015.

Peabody’s lenders are pushing it to restructure its debt through bankruptcy.

Peabody’s efforts to raise funds through asset sales hit a roadblock last month. A deal to raise $358 million in cash by selling coal mines in New Mexico and Colorado was temporarily shelved after the buyer failed to secure financing.

Peabody’s shares have crashed from their record high of more than $1,300 in 2008 to $2.36 on Wednesday morning. Its market capitalization was $74 million Wednesday, down from over $20 billion in 2008, according to Thomson Reuters data.

Fellow coal miner Foresight Energy LP FELP.N said on Tuesday it may file for Chapter 11 bankruptcy if it does not reach an out-of-court restructuring agreement with its lenders.

Patriot Coal Corp, which was spun off from Peabody in 2007, filed for bankruptcy protection in May 2015, just 18 months after emerging from its previous Chapter 11.

Other coal miners that have filed for protection include Walter Energy WLTGQ.PK and Alpha Natural Resources Inc WLTGQ.PK.

Cloud Peak Energy Inc CLD.N, Consol Energy Inc CNX.N, Foresight and Westmoreland Coal Co WLB.O were all lower by about 1 percent in midday trading on Wednesday.