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The mining levy was introduced in 2012 by PiS's predecessors in an attempt to improve the state budget.
Calculated using a complicated formula based on local production volumes, the tax primarily affects KGHM, one of the world's biggest copper and silver producers, which has struggled with rising costs.
Poland holds a general election later this year. PiS promised to lower the tax ahead of the last such vote in 2015, but so far no cut had been implemented.
KGHM is a major employer in southeast Poland and reducing the tax would be a welcome move for many voters in the region.
KGHM paid 1.67 billion zlotys ($442 million) in mining tax in 2018, while the group's net profit was 1.66 billion zlotys.