The Financial Post reports in its Saturday, Dec. 7, edition that the rules governing the use of steel and aluminum in cars have emerged as the latest obstacle to completing a revised North American trade deal between the U.S., Mexico and Canada in time for congressional approval by year-end. A Bloomberg dispatch to the Post reports that the three nations are discussing the fine print of the agreement that requires 70 per cent of steel and aluminum in vehicles to come from the continent in order to receive duty-free treatment, according to several unnamed sources. Mexico and the U.S. administration are seeking to agree on changes to the text as early as Friday before presenting a proposal to House Democrats. Last week the U.S. put on the table a demand to count only steel and aluminum slab toward the 70-per-cent threshold that originate in North America, sources said. That would complicate qualification for cars produced in Mexico, where slabs often originate in Brazil, Japan and Germany. The proposal was floated as a demand from the United Steelworkers union last year, two sources said. On Monday, President Donald Trump announced plans to reinstate tariffs on steel and aluminum from Brazil and Argentina.