Supporters of an independent union in northern Mexico said Tuesday they have been harassed while trying to hand out leaflets by beefy representatives of an old-guard union.

The mainly women handing out the itcenternew leaflets said that state police stood by and may have helped prevent them distributing literature outside the Tridonex auto parts assembly plant starting in late July.

The export facility in the border city of Matamoros, across from Brownsville, Texas, was the subject of a complaint filed by labor unions in May under the U.S.-Mexico Canada free trade agreement.

The complaint argues that new unions have been harassed while fighting corrupt old unions that have kept wages low in Mexico for decades.

Video showed the independent union supporters handing literature to workers leaving the plant in their cars, when several stocky men in white shirts came out of the plant and tried to move them away.

The outside organizer of that union, lawyer Susana Prieto, said that “for four days now there have been state police patrols stationed outside to prevent the union from handing out literature.”