Zimbabwe Prime Minister Morgan Tsvangirai has accused the party of President Robert Mugabe of bad faith in the new unity government, and of persecuting his group.
Addressing a rally in Bulawayo to celebrate the 10th anniversary of his Movement for Democratic Change party, Mr Tsvangirai said he would not stand by while Zanu-PF violated the law.
He told his supporters that he wanted partners who are going to commit themselves to good governance principles.
"We cannot have partners of looters," he said.
The BBC reports the speech was one of the rare signs of frustration that the MDC leaders has shown in public with Zanu-PF since forming the government of national unity in February.
The alliance was created to try to end the political turmoil that followed disputed elections last year.