Pro-democracy campaigners in Hong Kong vowed Friday to take to the streets in protest over what they said was China's fiercest assault on the city's treasured autonomy with its move to impose a security law. The proposal for the legislation -- expected to ban treason, subversion and sedition -- was introduced into China's rubber-stamp parliament at the opening of its annual session on Friday morning. It followed repeated warnings from China's communist leaders they would no longer tolerate dissent in Hong Kong, a semi-autonomous city that endured seven months of massive pro-democracy protests last year.