The Industrial Union has announced new political strikes in early February that will see some 60,000 workers across 700 locations walk out for two days starting on 1 February.
The strikes have been called in protest at government plans to legislate on labour market rules and cut social security benefit payments.
Among other proposals, the government is planning to eliminate the automatic entitlement to sick pay from the first day of sick leave.
Companies hit by the new strike warning include UPM, Metsä Fibre, steel firm SSAB and the Meyer Turku shipyard.
In December the union had announced that Neste's oil refinery in Porvoo will shut down during the strikes. The white-collar Pro union is also striking on the same dates.
Union leader Riku Aalto said that he feared the government's plan to bring in new spending cuts as a response to worsening economic forecasts might also end up costing his members.
"The government programme includes measures that are directed at workers," said Aalto. "Our fear is that the new, extra spending cuts might target the same groups as before."
Prime Minister Petteri Orpo (NCP) criticised the union's announcement.
"These [strikes] are excessive and cause big losses to the Finnish economy," said Orpo. "I would hope that we could avoid such large strikes."
Users with an Yle ID can leave comments on our news stories. You can create your Yle ID via this link. Our guidelines on commenting and moderation are explained here.