Cape Town - Democratic Alliance chief whip John Steenhuisen has written to Speaker of Parliament Baleka Mbete, demanding that she make her decision on the secret ballot by 09:00 on Saturday.
Parliament is still waiting for Mbete to make a decision on the use of a secret ballot in the motion of no confidence in President Jacob Zuma on Tuesday.
The Constitutional Court ruled in June that Mbete, as Speaker, does have the constitutional power to decide whether or not to hold a secret ballot during the motion.
Steenhuisen sent a letter on Friday, after receiving no reply to a previous letter sent the day before.
"It is now two working days before the scheduled vote, and you have still not communicated your decision," he said.
"You plainly have not complied with your own commitment to take the decision 'at the earlier opportunity'."
He said Mbete has had long enough to decide, since she asked parties to make submissions on the secret ballot on July 14, and was acting in bad faith.
Steenhuisen claimed Mbete's delay was a "naked attempt" to either frustrate opposition parties from challenging a possible open vote decision in court, or to ensure the motion itself was delayed.
He said the party would take further legal action if Mbete did not announce her decision by 09:00 on Saturday.
Parliament spokesperson Moloto Mothapo told News24 this week that the Speaker had not communicated a date for the announcement of her decision yet.
She previously said she would make her decision known before the August 8 vote, he said.
African National Congress chief whip Jackson Mthembu on Friday said that ANC MPs would not support the DA-sponsored motion to remove Zuma as president.
Voting in favour of the motion of no confidence in Zuma would be like "throwing a nuclear bomb at the country," Mthembu told reporters in Parliament.
"The removal of the president will have disastrous consequences that can only have a negative impact on the people of South Africa," he said.
It would result in the entire Cabinet having to resign, and a collapse in government.
The sitting next week is due to sit from 14:00 on Tuesday. Three separate marches are due to take place next week; one on Monday and two on Tuesday.