Democratic Alliance leader Mmusi Maimane says they will consider legal action unless National Assembly Speaker Baleka Mbete approves an hoc committee inquiry into state capture by the end of October.
Maimane released a statement on Sunday following his party's final federal council gathering of the year in Tshwane.
He said that while the DA welcomed Parliament's Public Enterprises Committee's probe into state capture in several state-owned enterprises, it still wanted a "centralised ad hoc committee on state capture".
The DA has written to Mbete, asking her to implement this by October 31.
"We have written to the speaker of the National Assembly in this light, giving her until 31 October to do so, failing which we will consider the appropriate legal action."
In other areas, Maimane also said he has written to National Director of Public Prosecutions Shaun Abrahams to have the outstanding charges against President Jacob Zuma reinstated, as upheld by the Supreme Court of Appeal.
He also said the party's current impasse between Cape Town mayor Patricia de Lille and mayoral committee member for safety and security JP Smith will be concluded in 14 days.
Opposition parties to meet with IEC
Opposition party leaders meanwhile will meet with the IEC next month - in the run up to the 2019 elections, he said on Sunday.
"Leaders of opposition parties will be meeting with the Independent Electoral Commission (IEC), in order to discuss a number of matters," said DA leader Mmusi Maimane in a statement.
"These include the independence of the IEC, an update on the investigation into the ANC's infamous 'black ops' operation, the appointment of the new IEC CEO, and ensuring that the 2019 elections are truly free and fair."
The meeting would take place on November 15.
He noted that at the meeting report backs had been given about the current political coalitions and "working partnerships" in which the DA was involved.
"Our coalitions and partnerships are stable and functional," he declared, adding that in Port Elizabeth, "all coalition partners are back on board".
There has been previous tensions between the DA and certain coalition partners at the Nelson Mandela Bay municipality, following the ousting of deputy mayor Mongameli Bobani, who was a UDM councilor.
He lastly congratulated the party's student organisation representatives, DASO, at the University of Cape Town who won the majority of seats at the student representative council elections.