Hewlett-Packard, the world's largest computer maker, has tightened hiring rules for Chinese suppliers two weeks after Apple said an employment agent on the mainland forged documents on behalf of underage workers. Working hours for students must be lower than the legal limit and the total number of student workers must also be limited, HP said yesterday. Suppliers must comply with the guidelines immediately, said the maker of Envy laptops and other peripherals. The effort to improve working conditions follows Apple, which joined the Fair Labour Association last year after being criticised for working conditions at suppliers including Foxconn Technology Group. Foxconn, which supplies both computer makers, said HP's new guidelines don't impose any requirements beyond what it already does. "We don't hire outside contract workers," Louis Woo, spokesman for Taipei-based Foxconn, said yesterday. "It's been our policy for a long time not to allow student interns to do overtime or night shift, and we pay them the same as any other entry-level workers." Apple stopped doing business with a manufacturer that employed 74 people younger than 16 who used faked papers, the Cupertino, California-based company said in its annual supplier responsibility report released on January 25. HP said suppliers must ensure "fair remuneration and social insurance" and all work should be voluntary. "Local regulations must be reinforced or exceeded," the Palo Alto, California-based firm said. "Student workers should only engage in work activities that complement the primary degree they are seeking to obtain." Students and temporary workers must be free to leave work upon reasonable notice without negative repercussions, and they must have access to reliable and reprisal-free grievance mechanisms, the HP rules state.