The Movement for Democratic Change has for the first time threatened it could disengage from the agreement that brought about Zimbabwe's unity government.
The MDC statement was made during a news conference hastily convened after the weekly Zimbabwe Cabinet meeting was moved forward from its usual time later in the week.
Deputy Prime Minister and MDC vice president Thokozani Khupe explained why the Movement for Democratic Change decided to boycott the early meeting.
"The decision seeks to deny the recognition of the Prime Minister as chair of the Cabinet when the president is away," she said. "Mr. Mugabe has indicated that he will not be present on Tuesday and hence the unilateral decision to move cabinet forward to today. However, whilst we remain fundamentally committed to the GPA [power sharing agreement] in the interests of our people, it is our constitutional right to consider disengagement."
Ms. Khupe said MDC leader and Prime Minister Morgan Tsvangirai should have chaired the meeting in President Robert Mugabe's absence. She said Mr. Mugabe's Zanu-PF party "has not welcomed MDC as an equal partner.
Khupe said despite five months of meetings, issues such as the future of the central bank governor, the attorney general, the swearing in of deputy minister Roy Bennett and provincial governors, and the appointment of ambassadors remain unresolved.
The governor of the central bank is blamed for his part in the near collapse of Zimbabwe's economy, while the Attorney General is accused of being a supporter of Mr. Mugabe's party and biased in its favor.
The MDC wants both replaced, while Mr. Mugabe has vowed they are going nowhere.
Khupe said these and other outstanding issues have been referred to the Southern African Development Community, the regional body that helped negotiate the Unity Agreement.
The statements in Harare were made despite pronouncements by Prime Minister Tsvangirai, during his recent trip abroad, that all is well in the unity government. He returned to Harare on Monday.
Mr. Mugabe is barred by international travel restrictions from visiting the countries on Mr. Tsvangirai's itinerary. The leaders with whom the prime minister had cordial talks - among them U.S. President Barack Obama - accuse the former Mugabe government of trampling on democracy and ruining a once-vibrant economy.
Zimbabwe's state-run Herald newspaper has reported some Zanu-PF officials were worried about Mr. Obama's reference to building a new partnership, not with the coalition government, but with Mr. Tsvangirai, a former opposition leader who was once beaten and jailed by the Mugabe government.