The reinstatement of Brian Molefe as Eskom CEO places him in a "position to frustrate or obstruct" any investigations against him, the Democratic Alliance (DA) says in court papers.

The party on Monday brought an application in the High Court in Pretoria, asking it to rule Molefe's reinstatement by Public Enterprises Minister Lynne Brown irrational and unlawful.

It firstly wants the court to interdict Molefe from performing any duties or functions as Eskom CEO and from receiving any benefits associated with the position and, secondly, to set aside his appointment.

"The Public Protector and the Minister have called for full investigations into transactions overseen by Mr Molefe. The reinstatement of Mr Molefe to the position of Group Chief Executive places Mr Molefe in a position to frustrate or obstruct any such investigations against him," DA federal executive chairperson James Selfe says in the affidavit.

Molefe's reappointment, and subsequent resignation as African National Congress MP, came to light on Friday. Brown said reappointing Molefe "represents a significantly better value proposition to the South African fiscus" than a R30-million pension payout.

She said the R30-million figure was reached in terms of the provisions of Eskom's pension fund, governed by the Pensions Fund Act.

"The appointment/reinstatement of Mr Molefe is in breach of the requirements of the relevant legal framework and is irrational," Selfe says.

"The minister ought instead to have accepted neither the proposal of payment of R30-million in pension benefits to Mr Molefe, nor the proposal that he be reinstated to the position of Group Chief Executive at Eskom.”

Had Brown acted lawfully and rationally, she ought to have rejected both options as unjustifiable and unlawful.

Selfe disputes that Molefe went on early retirement, as he was 50 and not 55, and even if he had gone on early retirement, a R30-million pension payout would be "inconceivable".

Brown, Molefe and Eskom are the respondents in the matter, which the DA wants to be heard on May 30. They are expected to file responding affidavits by Wednesday.