WARSAW (Reuters) - Polish state-run power producers will halt coal imports, State Assets Minister Jacek Sasin said on Tuesday, after protests by mining trade unions over foreign supplies they say are a threat to the domestic industry.

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Poland generates most of its electricity from coal, but domestic output has fallen because of cost-cutting and geological problems in old mines, which had led to higher imports, mostly from Russia.

Last week around 100 miners blocked trains carrying coal to a power plant in the southern town of Laziska Gorne in protest at imports from Russia by state-run energy groups, including PGE and Tauron.

Unions said increased imports, together with falling demand following a mild winter, have increased coal stockpiles, threatening normal operations of Poland’s coal mines.

“Energy groups had been forced to import coal, because there was none in Poland. Now the situation is different and I can declare they will no longer buy coal from abroad. We want to focus on Polish coal first of all,” Sasin told private radio RMF FM.

PGE is contractually obliged to import some coal, he said, without specifying how much, but said supplies for this year have been frozen.

Sasin also said the government cannot ban coal imports for private companies, for which the imported coal is cheaper and of higher quality than domestic production.

“What we can do is rationalize the situation in (Polish) mining firms, so that the coal is cheaper, so that better quality coal is produced,” Sasin said.

Trade unions at Poland’s biggest coal mining firm PGG have not ruled out a strike to demand a pay rise and address the issue of stockpiles.

In 2018 Poland imported almost 20 million tonnes of coal. Between January and September 2019, imports totaled 12.3 million tonnes, including 8 million from Russia.

Critics say this was at odds with the ruling Law and Justice (PiS) party’s aim to reduce Poland’s reliance on Russian fuel imports.

Poland is also under pressure from the European Commission to use less coal.

More than 90% of Poles think the climate is changing and almost 64% believe Poland should stop using coal in power generation to reduce emissions, a poll by United Surveys for radio RMF FM and Dziennik Gazeta Prawna daily showed on Tuesday.