Poland relies on coal for almost 80% of its electricity production, but lockdown measures, which have shut schools, restaurants, cinemas, some factories and reduced railway transportation, have led to a decrease in electricity usage that the company puts at 10-12%.
"We need to protect the company and prepare solutions for the future when we overcome the pandemic and the economy accelerates again," Chief Executive Tomasz Rogala said in a statement.
A PGG spokesman said the company did not yet know how much output would fall as a result of the changes.
The reduction in working time, which would apply to all employees, would allow PGG to apply for funding under the government's economic support programme of about 70 million zlotys ($16.91 million) a month, the company said.
(Reporting by Wojciech Zurawski, Alan Charlish and Anna Koper; editing by Barbara Lewis)