MEXICO CITY (AP) — Mexico's Senate has approved a labor law overhaul aimed at ensuring workers can freely vote for their union representation and contracts.

The new law requires secret-ballot union votes and proof of workers' consent for contracts. The changes are needed to win approval of the new U.S.-Mexico-Canada trade agreement, which was negotiated to replace the old NAFTA accord.

Mexico's labor movement has long been stymied, and wages kept low, by pro-government unions that sign contracts and organize plants behind workers' backs.

Since President Andres Manuel Lopez Obrador took office Dec. 1, labor unions already have staged a wave of strikes and formed new federations to take advantage of the greater freedom.

The bill approved Monday night now goes to the president to be signed into law.