WASHINGTON — President Trump’s ability to get his revised North American Free Trade Agreement through Congress may hinge on a little-noticed provision governing intellectual property protections for new pharmaceutical products.

Congressional Democrats have seized on measures in the United States-Mexico-Canada Agreement that establish protections for drug companies, saying they are a boon to the pharmaceutical industry and could undermine efforts to make American health care more affordable.

The issue is the latest complication in Mr. Trump’s yearslong effort to rip up Nafta and rewrite the rules of trade with Canada and Mexico. While Mr. Trump secured Canada’s and Mexico’s signoff on the new agreement last year, the trade pact must be ratified by legislators in all three countries, including by Congress.

Democrats, who now control the House, have already made it clear that they will not approve the new trade deal without significant changes to labor and environmental provisions. Now, they are also looking for revisions to the trade deal’s pharmaceutical provisions, in particular a measure providing an advanced class of drugs called biologics 10 years of protection from cheaper alternatives.