Talks between the United States and Canada on a long-running dispute over softwood lumber exports have bogged down amid “significant differences,” the two nations said on Friday, potentially paving the way for a fresh round of lawsuits.

U.S. producers complain that Canadian lumber is subsidized, and have in the past launched trade challenges that resulted in the United States imposing billion of dollars in tariffs.

The most recent round of arguments ended with a 2006 deal that expired in October 2015. Both sides agreed to take no action for a year after that, but without a new treaty, U.S. firms have made clear they will file new damage claims.

In March, President Barack Obama and Prime Minister Justin Trudeau asked officials to work out possible solutions and report back within 100 days. That deadline runs out on June 18.

“Significant differences remain between us,” said U.S. Trade Representative Michael Froman and Canadian Trade Minister Chrystia Freeland in a joint statement.

“The United States and Canada have made significant advances in exploring the key issues and priorities …(and) are committed to continuing negotiations.”

Reuters reported on June 10 that the talks were making little progress. Canadian officials say one challenge is that domestic producers are split over the best strategy.

BC Lumber Trade Council Chief Executive Susan Yurkovich said she believes an agreement can be reached that will provide certainty for lumber producers on both sides of the border.

“However, if a reasonable agreement cannot be reached, we are also prepared to work alongside the Canadian government to defend the industry against any potential trade actions brought by the United States,” Yurkovich said in a statement.

Major Canadian lumber firms include Canfor Corp CFP.TO, West Fraser Timber Co WFT.TO, Interfor Corp IFP.TO and Resolute Forest Products Inc RFP.N.