Canadian officials are using negotiations over the North American Free Trade Agreement to press the U.S. to pass a federal law banning states from having right-to-work laws that say workers cannot be forced to join or support a union as a condition of employment.

Canada says the laws put its own businesses at too much of an economic disadvantage compared with the U.S.

The U.S. is opposing the request, which was reported by the Toronto Globe and Mail citing "one source familiar with the discussions." A spokesman for the U.S. Trade Representative's Office could not be reached for comment. President Trump said during the 2016 presidential campaign that he supports right-to-work.

State right-to-work laws prohibit union management contracts that require all workers either join the union or pay it a regular fee or else lose their jobs. The provisions, dubbed "security clauses" by unions, are common in states without the laws. Unions argue the money pays for collective bargaining expenses that benefit workers. Business groups and Republicans back right-to-work laws, arguing they give states an edge in attracting business and that joining a union should be up to the workers.

A total of 27 states currently have the laws. Five states have adopted them since 2012, including Michigan and Wisconsin, both of which border Canada. Missouri passed legislation, but it is on hold pending the outcome of a voter referendum. Several of the laws date to the 1940s, when they were first allowed by the 1947 Taft-Hartley amendents to the National Labor Relations Act. Prohibiting them would severely disrupt business practices in those states.

Canada's stance is being pushed by its unions. "I'm very pleased with the position the Canadian government is taking on labor standards. Canada's got two problems: The low wage rates in Mexico and the right-to-work states in the United States," Jerry Dias, head of Unifor, Canada's largest private-sector trade union, told reporters in Mexico City last week, where the second round of talks are being held.

A spokesman for the Canadian Embassay could not be reached for comment.

Advocates for the law found the Canadian government's position outrageous. "Right-to-work doesn't stop a single worker from joining or paying dues to a union, it just protects the individual rights of each worker to decide for him- or herself if payment of dues is what is best for themselves and their family. Further, we know that once you adjust for the cost of living, workers in right-to-work states have $2,400 more in disposable personal income than workers in states with forced union dues," said Patrick Semmens, spokesman for the National Right To Work Legal Defense Foundation.