On Monday the PGG miners held a two-hour warning strike to demand a 12% increase in salaries and a clear national energy plan guaranteeing a future role for coal. The trade unions threatened that if there is no agreement with PGG management and the government, PGG miners will protest in Warsaw on Feb. 28.

"We signed an agreement with PGG trade unions. It assumes that salaries for PGG employees will rise by 6% as of Jan.1," State Assets Minister Jacek Sasin, who supervises the coal industry, said. "The protest in Warsaw will not take place."

Poland's ruling Law and Justice (PiS) party has taken steps to improve air quality and encourage investment in offshore wind and solar energy, but its plan regarding the nation's future energy mix is unclear.

The party, which is keen to secure coal miners' votes in a presidential election in May, has said Poland will continue to use coal as its main fuel for years to come.

PiS rose to power in 2015 partly on promises to sustain the then troubled coal mining. Since then the industry has recovered, as coal prices rebounded and the government closed some of the most loss-making mines.

Last year, however, the Polish coal industry started to face new problems because of increased coal imports and falling demand, leaving coal-mining companies with unsold stocks.

PGG does not disclose its financial results, but last week state-run utilities PGE, Enea and Energa, which all have minority stakes in PGG, said their 2019 results had been hit by impairments at PGG.

(Reporting by Wojciech ?urawski; writing by Agnieszka Barteczko; editing by Barbara Lewis)