When a nine-month investigation found he had recruited for the opposition DA, UDM regional secretary Bonginkosi Madikizela resigned before he could be dismissed, claimed UDM provincial secretary Bongani Maqungwana.
"He has been a party member since February 2007 and was elected regional secretary for the Cape Town metro in August. We've been investigating him and received information from members that he and six others were recruiting and campaigning for other parties.
"We got evidence he was busy recruiting UDM members for the DA. He also had dual membership and that is why we expelled him."
Maqungwana claimed by the time the UDM provincial executive decided on expulsion Madikizela resigned.
"We treat that as an admission of guilt."
Madikizela, now working as a media liaison officer in Cape Town mayor and DA leader Helen Zille's office, rejected the allegations.
He said his resignation was out of frustration with internal squabbles and the party's lack of organisation.
Madikizela joined the DA on Thursday.
Maqungwana said information about Madikizela recruiting for the DA had not been available when he was elected regional secretary.