The University of Hong Kong will start a referendum tomorrow to decide whether its student union should continue to be part of the Hong Kong Federation of Students. But 10 former presidents of the union called on members to cast 'no' votes, saying a split would undermine the unity of local universities in pursuing social justice. The referendum was initiated by a petition in September by several former and current HKU student union executive committee members critical of the federation's budget and internal disputes. 'The referendum is a good opportunity to let [our] schoolmates know this and then let them decide,' HKU student union president Lau Fong said. Chan Kai-yip, president of the student union last year, said the referendum would be the best way to deal with the situation by giving the decision back to students. Mr Chan came under fire in summer when he told other federation members not to tell the media about a meeting with Chief Executive Donald Tsang Yam-kuen. Representatives from Chinese, Polytechnic and Lingnan universities and Shue Yan College boycotted the meeting. But Gloria Chang Wan-ki, president of HKU student union in 2000, said the referendum was a bad move showing the union chose to quit rather than solve the problem. Rosa Mok Pui-han, HKU student union president in 1995, said if the union withdrew from the federation it would isolate the school from other institutions. The federation said last night it respected the HKU Student Union's decision to hold the referendum. Andrew To Kwan-hang, federation secretary-general from 1989 to 1990 and now a district councillor, said HKU's withdrawal would lead to a 'lose-lose' situation. He said the referendum had proven speculation that the central government had been trying to undermine the federation for a few years because it was a major opposition force in the city.