The union for Finnish paper workers has now extended the strike on the company UPM, the company writes on its website.
The strike would have lasted until January 22 but is now expected to continue until February 5 unless the parties agree.
The situation also has consequences in Sweden because UPM accounts for half of the paper that Swedish magazines use, it is so-called coated paper.
The magazines have tried to ship out as much paper as possible before the turn of the year, and find alternative suppliers.
But the autumn paper shortage makes the situation even more difficult as demand for paper has risen throughout Europe.