SEOUL (Reuters) - South Korea’s embattled President Park Geun-hye faces a pivotal week, with an effort to impeach her gaining support from within her own party and the heads of the country’s biggest business groups set to give testimony to a parliamentary committee.

South Korean President Park Geun-Hye speaks during an address to the nation, at the presidential Blue House in Seoul, South Korea, 29 November 2016. REUTERS/Jeon Heon-Kyun/Pool

Three opposition parties introduced a bill on Saturday to impeach Park, who is accused of abuse of power, putting her in danger of becoming the first democratically elected South Korean leader to leave office early.

“The chances of the impeachment bill passing on Dec. 9 are 50-50,” Woo Sang-ho, parliamentary leader of the main opposition Democratic Party, told a party meeting on Monday.

The vote is set for Friday. If successful, it would require the approval of South Korea’s Constitutional Court, a process that experts said would take at least two months.

The opposition parties need at least 28 members from Park’s Saenuri Party to secure the two-thirds majority required for the bill to pass. At least 29 of them are believed to be planning to vote for the bill, members of the breakaway faction said.

On Monday, Park’s presidential Blue House aides addressed a parliamentary hearing over the allegation that Park and her friend, Choi Soon-sil, as well as a senior aide to Park, put pressure on conglomerates to pay money to foundations that were set up to promote Park’s policy initiatives.

The heads of nine conglomerates, or chaebol, including Samsung Group’s [SAGR.UL] de facto leader Jay Y. Lee and Hyundai Motor Group Chairman Chung Mong-koo, have been invited to Tuesday’s inquiry, in what would be an unprecedented parliamentary appearance by such a group.

They are expected to be questioned whether they came under pressure from Park and were promised favors in return.

Park has denied wrongdoing but has apologized for carelessness in her ties with Choi.

Park was expected to make another public address this week, South Korea’s Yonhap News Agency cited ruling party officials as saying, although the presidential office said nothing had been decided.

In televised remarks last week, she offered to step down and asked parliament to decide how and when she should leave office.

Opposition parties rejected the proposal, calling it a ploy to buy time and avoid being impeached, and vowed to push ahead with impeachment.

They cited another protest rally on Saturday, which organizers called the largest yet, with 1.7 million participants, as the clearest reason why she should be ousted. Police said the Seoul crowd reached 320,000 at its peak.