As dairy products, Bombardier aircraft and softwood lumber continue to bedevil trade relations between Canada and the U.S., negotiators will have to add wine to their list of issues to resolve.

The U.S. has filed a second complaint with the World Trade Organization over what it perceives as B.C.'s unfair rules regarding wine sales in the province's grocery stores, according to a release from the WTO.

In the complaint, the U.S. argues that local wines have an unfair advantage in B.C. due to the province's rules that ban imported wine from grocery store shelves.

The rules dictate that imported products are relegated to a "store-within-a-store" model, separate from B.C. products and therefore appear discriminatory and inconsistent with a WTO agreement, according to the complaint.

The U.S. first raised the issue in January, but according to the WTO website no dispute panel was established and they were not notified of either a solution or withdrawal by the parties.

"British Columbia's discriminatory regulations continue to be a serious problem for U.S. winemakers," United States Trade Representative spokeswoman Amelia Breinig said in an email. "USTR is requesting new consultations to ensure that we can reach a resolution that provides U.S. wine exporters fair and equal access in British Columbia."

The B.C. Ministry of Jobs, Trade and Technology and The Office of the United States Trade Representative did not immediately respond to a request for comment.

The province's previous trade minister, Shirley Bond, said the government will defend the industry against the challenge when it was first issued in January.

The issue of selling wine, beer and spirits in Canada has been a flashpoint for American producers for some time.

The U.S. government's annual report on trade barriers highlights restrictions on listings, cost-of-service mark-ups, maximum or minimum price points, distribution policies, labelling requirements and making suppliers discount their prices to meet sales targets as areas of concern.

The report said the U.S. government is reviewing the situation in Ontario, where about 70 grocery stores are now allowed to sell both domestic and imported wine, under certain conditions that include country of origin.

It also suggested a recent move to allow Quebec wine to be sold in Quebec grocery stores could give craft wineries an unfair advantage.