The Swedish Paper Workers Union said a further 2,800 workers could join the 10-day strike that already includes 3,000 workers.
“At 6pm tonight, another six plants with 2,800 workers could join the strike,” Mikael Sterbaeck of the union told AFP.
He added the strike extension could still possibly be avoided as last-minute talks were still ongoing after collective agreement negotiations broke down at the weekend.
Some 3,000 paper mill employees have been on strike in six Swedish paper mills since April 16th, and on Monday morning a seventh plant counting 60 employees shut down due to the strike.
The Swedish Forest Industries Federation said at the weekend the strike had cost it more than 510 million kronor so far, and that if the planned extension of the work stoppage went ahead, it would begin bleeding around 100 million kronor per day.