Migrant groups are calling on the incoming SAR government to ratify a United Nations convention which guards against exploitation of foreign workers. With placards and loudhailers, some 30 migrant worker representatives yesterday marched from Chater Garden, Central, to Citibank Tower with a petition for the Chief Executive-designate, Tung Chee-hwa. Asian Migrant Centre training co-ordinator Rex Varona said workers wanted more than just a verbal assurance that maids can stay after June 30. The petition calls on Hong Kong to ratify the United Nations Convention for Migrant Workers which spells out labour rights, living and working conditions and makes airing grievances easier. 'The issue isn't just about what will happen after 1997 - but that even now workers are vulnerable.'