"As a Chapter Nine institution, the public protector should be totally independent of government, responsible only to obey the Constitution and the law..." said spokesperson Linda Yates.
"Government should uphold the independence, impartiality, dignity and effectiveness of the public protector."
She said delegates at the party's national convention noted that increasing pressure had been being exerted on Madonsela by those opposed to the release of the Nkandla report.
Last month, the Mail & Guardian reported that Madonsela had found in her preliminary report that President Jacob Zuma had misled Parliament, and had benefited substantially from a R206m upgrade to Zuma's homestead in Nkandla, KwaZulu-Natal.
Earlier this year, Public Works Minister Thulas Nxesi classified the report, saying it would put Zuma's safety at risk if released.
According to the newspaper, the report found that the upgrades had nothing to do with security features and included a swimming pool.
The story led to the ANC accusing Madonsela of leaking the report.
Madonsela condemned the leak.
A parliamentary committee's findings on the report indicated that it exculpated Zuma, finding no evidence that taxpayers' money had been used to pay for his private home - as he has insisted in statements to the National Assembly.
Earlier this month, Cabinet ordered the release of report but it had been delayed.
