Sheikh Hasina Wajed, the opposition leader, told a rally on the steps of the parliament building in Dhaka, the capital, that she would lead "a fierce campaign to bring down the government".
Bangladesh has already been crippled by 40 days of strikes and often bloody unrest. Diplomats contacted in Dhaka said the walk-out by opposition MPs could unleash even more riots and street clashes between supporters of the rival politicians. An eight-hour general strike has been called for today.
Ms Zia's rivals are demanding that she step down before her term ends in 1996 and turn the country over to an impartial caretaker president. It is still possible that the Prime Minister will accept these ultimatums. Bangladesh has been virtually ungovernable since last February, when the opposition began its boycott of parliament, complaining that the 1991 elections that brought Ms Zia's Bangladesh National Party to power were rigged.
"We've tried our best but without results," Ms Hasina told the rally. "The Prime Minister has shown utter disrespect for the people's plea for a clean vote." The personal animosity between the two women is tangled up with Bangladesh's post-independence
history. Ms Zia's husband was one of the military officers responsible for executing Ms Hasina's father, Bangladesh's first leader, before he, too, was killed in an army coup.
A corridor for compromise does exist, however. The Prime Minister has agreed to resign before the elections, but she has not specified when.
Nor was it agreed in heated talks between Ms Zia and the three main opposition parties - Ms Hasina's Awami League, the Islamic fundamentalist Jamaat-e-Islami party and the Jatiya Party, which backs the deposed former ruler, Hossain Ershad - who should sit in the caretaker cabinet. Ms Hasina is pushing for a cabinet with ministers picked from the main parties, but the Prime Minister is reported to favour a temporary government made up of non-politicians.
If Ms Zia chooses to fight it out, according to diplomats, she would have the constitution and her parliamentary majority on her side. One option is for her to hold by-elections in the empty parliamentary seats. Another is to ask President Abdur Rahman Biswas to dissolve parliament immediately and hold new elections.
Her rivals would prefer to wait a few months once her party has cleared out of government. That way, opposition MPs say, the ruling party would have fewer chances of cooking the election results.