HELSINKI, Finland – Finland’s paper industry remained crippled Wednesday as the start of a four-week lockout by employers closed most paper and pulp mills after labor talks with unions broke down. Finland accounts for 15 percent of the world’s paper production.

The government fears the dispute, which could cost hundreds of millions of dollars, will spread and have a negative impact on foreign trade and the economy. Talks were scheduled to resume Friday. The negotiations have continued for months.

The lockout and earlier strikes in the industry, including at some of the world’s largest paper makers, UPM-Kymmene Corp. and Stora Enso Oyj, could also raise global paper prices, analysts said.

The lockout is not affecting operations at Madison Paper Industries in Madison, Maine, said William Crane, corporate communications director for Myllykoski North America. The mill is a partnership of Finland’s Myllykoski Corp. and the New York Times Co.

“We’re running full out and there’s no effect,” Crane said.

Markets had been expecting the lockout, and helped by analysts’ predictions, forest industry shares surged on the Helsinki Stock Exchange. UPM’s shares closed up 2.6 percent at 15.77 euros ($19.90), while Stora Enso’s stock rose 2.7 percent to close at 10.66 euros ($13.45).

The lockout, originally planned to last two weeks, was stretched to a month by employers in a surprise announcement after Tuesday’s round of talks ended in deadlock.

Union chief Jouko Ahonen described the move as “militant,” and hinted the union might take further action after thousands of its workers closed factories for two days this week before the lockout began.

“This is pretty militant,” said Ahonen, who heads the 50,000-member Finnish Paper Workers’ Union. “But when the paper union goes on the attack, then you’ll see when a real war begins.”

Thousands of paper workers in neighboring Sweden ended a two-day overtime ban Wednesday, which had been imposed in support of the Finnish strike. The paper union said it expected similar action by other European workers.

The shutdown of some 50 paper, pulp and paper board mills was expected to hit other sectors and cause thousands of layoffs, including in the chemical industry that supplies products for forest companies. Road and ship transports would also be affected as exports of forest products stop. The southern port of Kotka said it had stopped using temporary employees as paper transports dwindled on Wednesday.

The government has said it will not interfere in the dispute. However, Trade and Industry Minister Antti Kalliomaki warned that the dispute would have “an extremely severe” impact on the economy. The forest industry accounts for 8 percent of gross domestic product and about a third of all Finnish exports.