FACTBOX: What's next in South Africa's crisis over Mbeki?

JOHANNESBURG (Reuters) - South Africa's ruling African National Congress (ANC) called on President Thabo Mbeki on Saturday to step down.

Mbeki has agreed to accept the ANC's decision once all constitutional obligations are met.

Here are some questions and answers on what is likely to happen next in South Africa's biggest political crisis since the country's first multi-race elections in 1994.

HOW CAN THE ANC PUSH OUT MBEKI?

A South African president can be removed if two-thirds of parliament supports a vote outlining he was guilty of a serious violation of the constitution or laws.

He can also be deposed through a vote of no confidence which needs just a majority.

But the process is more simple if Mbeki resigns -- parliament must then appoint a new president within 30 days. With the ANC's more-than-two-thirds majority in the National Assembly, this task should be a relatively easy process.

WHY DID THE ANC ASK HIM TO STEP DOWN?

Mbeki has been locked in a rivalry battle with ANC leader Jacob Zuma since 2005 when Zuma became embroiled in a corruption scandal. Mbeki fired Zuma as deputy president, enraging trade unions and rank-and-file ANC members.

The left was angry over Mbeki's pro-business policies and accused him of mounting a campaign to ruin Zuma's political career. Support from unions and members of the ANC youth wing helped Zuma defeat Mbeki for the ANC leadership late last year.

The infighting reached a climax last week when a High Court judge threw out graft charges against Zuma and suggested that high-level officials may have meddled in the case.

The prosecutors' decision to appeal the ruling further angered Zuma's supporters, who called for Mbeki to be fired.

WHO WILL REPLACE MBEKI?

According to the Constitution, Deputy President Phumzile Mlambo-Ngcuka could become president, but she has said she will step down should Mbeki be forced to leave office.

A cabinet minister or the speaker of the parliament could then be called on to lead a transitional government until an election is held. Zuma is widely expected to win the election and become president.

WILL THIS WORRY FOREIGN INVESTORS?