DA leader Mmusi Maimane on Saturday announced Zille's suspension from party duties pending the outcome of a disciplinary hearing for tweets she made about colonialism.
Provincial ANC secretary general Faiez Jacobs told News24 that the decision was long overdue.
"We commend the DA leader for his courage in doing this, but we think it's not enough," Jacobs said on Saturday.
"For too long, Zille's been handled with kid gloves."
Her previous comments on Twitter where she used the term "professional blacks", and once describing black people in the Eastern Cape as "refugees" was evidence she would not change.
Zille's comments have further alienated black voters, and it was an insult to only suspend her from party duties, but not as premier, he said.
"She will not change her spots, so the suspension is not enough."
They called on Zille to be suspended from all her government positions, and for her to resign.
It was Zille's tweets on colonialism that landed her in hot water.
The tweets read: "For those claiming legacy of colonialism was ONLY negative, think of our independent judiciary, transport infrastructure, piped water etc."
Another read, "Getting onto an aeroplane now and won't get onto the wi-fi so that I can cut off those who think EVERY aspect of colonial legacy was bad."
She later apologised for her comments, saying she never intended to defend colonialism.
Maimane told the media on Saturday that he had asked Zille to apologise for her tweets but she refused to do so. -- News24