Polish teachers have warned they could go on strike if pay negotiations with the government do not produce a compromise by January 10, according to reports.

The head of the Polish Teachers’ Union (ZNP), Sławomir Broniarz, said union officials have invited Prime Minister Mateusz Morawiecki for talks on January 7, Poland’s PAP news agency reported.

One of union’s main demands is a PLN 1,000 (EUR 233, USD 268) gross rise in monthly wages.

Teachers from several Polish cities began an informal protest on Monday, taking sick leave en masse.

bur/pk