Members of the Professional Teachers' Union have officially voted to dissolve the 48-year-old body.
At a special meeting on Saturday afternoon, more 130 members backed the decision, while six voted against and two abstained.
"With the worsening of the situation, this is a decision we have to make, actually we're quite sad about this," said the union's president, Fung Wai-wah, as he met reporters after the meeting.
The PTU is the largest union for a single profession, representing almost 100,000 members.
It announced its decision to disband last month, after the government said it would stop working with the union - accusing it of having encouraged students and teachers to join anti-government protests.
Prior to the government statement, the Xinhua News Agency and the People's Daily had criticised the union as a "malignant tumour". Following its dissolution announcement, the media outlets also urged the authorities to take action against the group.
"Actually we worry about the possible persecution, but we can't help it," said Fung.
He said he expects the union to take a few months to go through all the disbandment procedures, including the selling of its assets and staff redundancies.
Fung said he hoped there would be new groups to stand up for teachers and their rights.