Western Cape premier Helen Zille will face disciplinary charges for her social media remarks on colonialism, Democratic Alliance (DA) leader Mmusi Maimane announced on Sunday.

“The federal executive met today [Sunday] and made a decision to institute formal disciplinary steps against Ms Helen Zille,” Maimane told reporters in Cape Town. “This has not been an easy decision to take,” he said.

DA federal executive chairperson James Selfe said the decision to charge Zille with acting in a manner that brought the party into disrepute was however, a “very near unanimous one”.

She would not be suspended but remain in her post as premier while the disciplinary process unfolded. Selfe said this was the case because there was no danger that Zille would interfere with the probe or intimidate witnesses.

The charges follow a complaint lodged by Maimane, Zille’s successor and protege, after she posted a series of tweets last month in which she suggested that not every aspect of the legacy of colonialism was bad.

Maimane said it was not limited to this incident, though, and indicated that Zille had made matters worse for herself with her subsequent attempts to explain and defend her stance.

“The initial referral was supplemented on March 22 to include reference to “a series of comments [made] publicly and on social media that have… exacerbated and amplified the original tweet.”

This included an article she wrote for the Daily Maverick that appeared to repeat the initial, problematic view. In the article, Zille explained that she had returned from a visit to Singapore, where she was struck by the efficiency, to struggle to find milk or newspapers in the VIP lounge of OR Tambo Airport. She added that she had not defended colonialism but said its entire legacy was not negative.

“The tweeple had concluded that I had defended colonialism. Not so, I said, I had merely said that although it had been an oppressive and evil system, not every consequence had been negative,” she wrote.

Maimane recalled that he had personally laid the complaint that prompted an investigation that led to the decision to charge her, and said though he respected Zille and she had served the country with distinction he was pressing on with charges to defend the political party he led.

“I must protect the project and cannot tolerate any action by any person that seeks to undermine it. Preliminary evidence suggests that there is a strong case to answer,” Maimane said.

The issue should not be construed as one of free speech, since the charge was concerned with whether Zille’s statements harmed the party, had gone against its policies, or brought it into disrepute, he said.

Zille was to be informed of the decision to charge her immediately after the press briefing where it was announced.

It comes amid calls by Maimane for African National Congress leaders to join in a mass march by the DA next week against President Jacob Zuma and to support a vote of no confidence against him in Parliament, following the axing of finance minister Pravin Gordhan, among several other ministers and deputies, by Zuma around midnight on Thursday.