Opposition parties will approach the Electoral Court over Independent Electoral Commission (IEC) chairperson Pansy Tlakula's refusal to resign, United Democratic Movement (UDM) leader Bantu Holomisa said on Tuesday.

"[Lawyers] will file an urgent application which will be filed on Thursday morning or before," he said.

"It is no longer in our hands."

Opposition parties had given Tlakula until the close of business on Monday to respond to their call for her to step down.

Holomisa said she had not responded to them, which showed "how arrogant" she was.

Earlier this month, the parties said they were worried about the credibility of the May 7 elections. The parties met IEC management.

Parties calling for her resignation were the UDM, the Azanian People's Organisation, the African Christian Democratic Party, the United Christian Democratic Party, the Congress of the People, Agang SA and the Economic Freedom Fighters (EFF).

The Inkatha Freedom Party was originally named on the list of opposition parties but on Monday it said it was not part of the group.

Agang SA and the EFF had both indicated on Monday that they were still supporting the call for Tlakula to resign.

Last month, a forensic investigation by auditors PriceWaterhouseCoopers on behalf of the National Treasury on the procurement of the IEC's Riverside Office Park building in Centurion, Pretoria found that the process was neither fair, transparent, or cost-effective.

It also found that Tlakula did not give guidance or formally inform various people what was expected of them in the process.

Tlakula has maintained that the report did not accuse her of corruption.

The Treasury report followed a recommendation from Public Protector Thuli Madonsela in her own report into the matter, released in August 2013.

Madonsela found Tlakula had played a "grossly irregular" role in procuring the premises.

She recommended that Parliament consider taking action against Tlakula.

The complaint against Tlakula to Madonsela was lodged by Holomisa. Tlakula was CEO at the time the complaint was lodged.

The African National Congress on Tuesday said the call for Tlakula to resign was not genuine and based on the desire by some parties to delegitimise the elections.

"It is our belief that despite the threats of legal action being made, no competent court will accept the stated intention of forcing Advocate Tlakula to resign," spokesperson Jackson Mthembu said.

"Such a call we believe is illegal, unconstitutional and undermines the rights that advocate Tlakula, like any other citizen, enjoys in law."