Both leaders, he said from a moral aspect "must relinquish their posts. MCA must pick a leader who is not tainted so that he can gain the support of everyone. Then MCA can be united under one leadership."
The party EGM on Saturday passed a vote of no-confidence against Ong's presidency and only approved Chua as an ordinary member.
Dr Mahathir also reiterated his calls for MIC president Datuk Seri S Samy Vellu to step down.
"If he steps down, MIC will be given a new lease of life."