SHANGHAI - Police in Shanghai have started investigating a local garment firm after toxic dye was found in the school uniforms it manufactures, authorities said Monday.

Disciplinary supervision authorities are also investigating whether officials allowed the substandard uniforms to enter school campuses, a city government spokesman said.

As of Sunday, two out of 106 batches of school uniforms produced by the Ouxia Garment Company were confirmed to contain azo dye, which can cause cancer, said the spokesman.

Student uniforms for 41 schools in the city were produced by the firm or labeled with its "Ouxia" brand.

On February 18, education authorities ordered 26,400 primary and high school students to stop wearing Ouxia-brand school uniforms after a quality inspection campaign found toxic dye in some of the uniforms.

Education and quality inspection departments have strengthened inspections of school uniforms used in primary and high schools and asked all schools to deliver samples of their uniforms for quality testing before distributing them to students.