Taiwan's main opposition grouping on Wednesday approved an application by disgraced ex-president Chen Shui-bian to rejoin the party despite fears the move would damage its image.
Chen, who is serving a 20-year sentence for corruption, quit the Democratic Progressive Party (DPP) in 2008 after money-laundering allegations against him and his family surfaced.
He was sentenced to life in prison in 2009 but the term was reduced on appeal.
The 62-year-old applied in May to rejoin the party he once led. The application was approved by a screening committee.
Chen's supporters were overjoyed but the decision sparked criticism from within the party.
Former parliamentarian Lin Cho-shui said the move was "shameful" for an idealistic party.
It "would be a nightmare for the next DPP presidential candidate running in the 2016 race", Lin said.
Chen was convicted of corruption and money-laundering relating to his 2000-2008 terms in office.
He and his family were accused of laundering millions of dollars by sending political donations and secret diplomatic funds abroad, and of taking kickbacks on government contracts.
The ex-leader insists that the charges against him are part of a politically motivated vendetta by the current Kuomintang government, in retaliation for his years in power when he pushed for Taiwan's formal independence from China.
The scandal severely damaged the DPP and helped bring Ma Ying-jeou of the China-friendly Kuomintang to power in 2008. Ma was re-elected in January 2012.
Chen for several months was treated for depression and other health problems in a public hospital, but was then transferred to a prison hospital to continue serving his sentence.
Doctors have recommended home care for him, according to medical documents released by his office.
But the justice ministry has rejected the recommendation, angering Chen's supporters who accuse the Ma administration of a politically-motivated decision.