Under the resolution, Teksid, based in the northern border state of Coahuila, agreed to recognize an independent union and re-hire 36 fired workers.
The U.S. Trade Representative's office said in a statement that workers at the plant were previously denied their rights to choose their union and do collective bargaining. The factory, which produces iron auto parts, employs some 1,500 workers.
The case came to a resolution without a dispute panel or sanctions, Mexico's labor and economy ministries said in a separate statement. Teksid said it "diligently cooperated" with U.S. and Mexican officials during the process.
(Reporting by Daina Beth Solomon in Mexico City and David Shepardson in Washington; Editing by Leslie Adler and Christian Plumb)