© Reuters/REBECCA COOKFILE PHOTO: Logo of GM atop the company headquarters
(Reuters) -Three senior U.S. lawmakers on Tuesday asked General Motors Co to answer questions about reported labor rights violations at its Silao plant in Mexico, after the automaker's union there was accused of tampering with a worker vote.
House Democrats Dan Kildee, Bill Pascrell and Earl Blumenauer said in a letter to GM Chief Executive Mary Barra that the largest U.S. automaker "has a responsibility to speak out against violations of labor and human rights abuses at the Silao GM plant."
The lawmakers also said the company should ensure that its workers in Mexico do not experience threats or retaliation for speaking out.
GM did not immediately comment.
Mexico's labor ministry has said that some ballots were destroyed during a union-led April vote for workers to ratify their collective contract.
The vote is required under a Mexican labor reform to ensure workers are not bound to so-called "protection contracts." The reform underpins promises in the new United States-Mexico-Canada Agreement free trade pact to uphold worker rights.
(Reporting by David Shepardson and Daina Beth Solomon; Editing by Leslie Adler and Christian Plumb)