Zille’s party, the Democratic Alliance (DA), has referred the matter to the Federal Legal Commission for investigation after saying in her tweets on Thursday that the legacy of colonialism was not only negative.
She later apologised but opposition parties say it’s not enough.
A number of prominent DA members have condemned and pushed back against Zille’s comments.
Party leader Mmusi Maimane says Zille’s views are unacceptable and indefensible.
“Wed don’t subscribe to those views. I think those views are certainly not views that we stand for and they’re inconsistent with our values.”