South African Revenue Service (Sars) commissioner Edward Kieswetter says there is no legal proof that former president Jacob Zuma supports Public Protector Busisiwe Mkhwebane's subpoena for his tax records, according to a report in Business Day.

In court papers filed in the Gauteng High Court in Pretoria, Kieswetter said there was no evidence that Zuma's recent tweets, which seemingly gave Mkhwebane permission to access his records, were even authored by Zuma himself, the publication reported.

Kieswetter also questioned why Mkhwebane had not approached Zuma for his consent to access the records.

Mkhwebane is seeking Zuma's tax records from Sars as part of her investigation into allegations that, early in his presidency, he received undeclared payments from a security company, News24 earlier reported.

Sars, however, is unable to disclose taxpayers' information and it has lodged an urgent court application to prevent Mkhwebane from obtaining the records.

Mkhwebane denied that she was prohibited from accessing taxpayer information and said Section 7 of the Public Protector Act empowered her to do so.

She added that her attempts to obtain Zuma's tax records were not coercive and that Sars' refusal could amount to a criminal violation.

"It can never be seen as a threat by me to an applicant that its failure to co-operate has criminal consequences. By law, these violations attract criminal sanctions," she previously maintained.