Mexican garment workers have told a labour hearing in Toronto that despite safeguards in the 10-year-old North American Free Trade Agreement (NAFTA), they still work in unsafe conditions and face employer discrimination.

Their claims were backed by Canadian and US supporters, who told officials at the National Administrative Office-chaired hearing that a NAFTA-linked agreement aimed at protecting workers had failed to deliver.

"It makes many lofty promises, but the enforcement mechanism lacks teeth," Canadian lawyer Mark Rowlinson, representing the United Steelworkers of America, said of the North American Agreement on Labour Cooperation (NAALC) complaint process.

However, the Mexican workers said they hoped their complaints would lead Canada to order an investigation and ultimately force Mexico to enforce its own labour laws.

"I hope more than anything that the process takes these issues back to the Mexican government, and will ultimately mean the enforcement of labour rights," former Matamoros Garment factory worker Jaime Ayala Sanchez said.

According to the 23-year-old, employees at the now-closed plant worked without ventilation and emergency exits, had no access to drinking water or first aid supplies, and were forced to work overtime to meet high production quotas.

"The guard would close the doors and nobody could get out," she said.

Kevin Banks, the Canadian government official who chaired the hearing, said its purpose was to gather new information on Mexican labour issues in Mexico.

He declined to comment on criticisms of the NAALC process.