Anwar Ibrahim, Malaysia's prime minister-in-waiting for a second time, has accused the party of Prime Minister Mahathir Mohamad and "traitors" in his own camp of planning to bring down the ruling coalition and form a new one to deny him the premiership.
The brewing crisis is the latest chapter of the stormy relationship between Mahathir, 94, and Anwar, 72, that has dominated Malaysian politics for decades.
Here are key details of the feud:
1982 – As a rising young politician, Anwar joins Mahathir's party, the United Malays National Organization (UMNO), soon after the latter became prime minister for the first time.
1993 – Anwar rises rapidly in the party to become deputy prime minister, on course to succeed Mahathir.
1998 – Months of feuding with Mahathir over Malaysia's handling of the Asian financial crisis culminates in Anwar's sacking. In opposition, Anwar wins support from a large section of Malay Muslims, the dominant ethnic group in the multicultural country, to drive his Reformasi movement and Parti Keadilan Rakyat (PKR), or the People's Justice Party.
1999 – Anwar is convicted and jailed for corruption and sodomy, charges he maintains were politically motivated.
2003 – Mahathir steps down after 22 years as prime minister.
2004 to 2013 – Four years after his 2004 release, Anwar is again accused of sodomy by a male aide. Anwar says the accusations aimed at removing him from his post at the time, as leader of the opposition, which came close to defeating Najib Razak, another Mahathir protege, in the disputed 2013 election.
2015 – During Najib's administration, Anwar is jailed for sodomy for the second time.
2016 to 2017 – Mahathir quits UMNO amid calls for Najib to resign over a multi-billion dollar corruption scandal at a state fund. Mahathir forms a new party, Bersatu, before joining forces with Anwar's opposition coalition, Pakatan Harapan (PH).
He promises to seek a royal pardon for Anwar and hand him the premiership if the coalition succeeds in its bid to oust Najib and the UMNO-led government.
2018 – Mahathir leads the opposition coalition to an unprecedented victory in a May 9 general election, ending UMNO's 60-year rule. Within a week, Anwar is pardoned and released.
2019 – Anwar denies accusations of having sexually assaulted a former male aide, describing them as "politics at its worst". The case was dropped on grounds of insufficient evidence.
2020 – Mahathir faces pressure from Anwar's allies in the coalition to set a date for the handover, sources say. Separate meetings at the weekend between politicians from the ruling coalition and UMNO spark talks of a possible alliance to form a new government. Anwar blames the bid on "our former friends" in Mahathir's Bersatu and "a small faction of traitors" from his own party.