Georgian ex-Prime Minister Vano Merabishvili, a close ally of President Mikheil Saakashvili, has been detained and charged with corruption.
Prosecutors in the city of Kutaisi charged him with abuse of office, alleging his government paid activists to canvass for Mr Saakashvili's party.
Mr Merabishvili, who is still the party's chairman, was also charged with illegally acquiring property.
He reportedly denied the charges, which his allies dismissed as "political".
If convicted, he faces up to 12 years in prison.
The chairman of the United National Movement (UNM) served as Mr Saakashvili's prime minister for just four months, in the run-up to the October parliamentary election when the party lost in a shock defeat to allies of billionaire Bidzina Ivanishvili.
Before that, he held the post of interior minister for eight years, when he oversaw a crackdown on organised crime but was also accused of using excessive force against political protesters.
A former health minister, Zurab Chiaberashvili, was also arrested and charged with abuse of office. He also denied the charges, according to Georgian broadcaster Rustavi-2.
Mr Merabishvili is charged with putting UNM activists on the government payroll solely to canvass for the party at the election.
In addition, he is said to have misappropriated a luxurious private villa by intimidating its owner, while he was still serving as interior minister.
Giorgi Gabashvili, a senior member of the UNM, told Georgian media he believed Mr Ivanishvili, who is now prime minister, was himself behind the arrests.
"The decision by Ivanishvili to detain Merabishvili and Chiaberashvili is a purely political one but they will fail to destroy the [UNM]," he told Georgia's InterPress news agency.
"The current government has made a very bad mistake."
Some members of the previous government were dogged by allegations of abuses of power for years - cases which, according to rights activists, were insufficiently investigated during almost a decade of unopposed rule.
Since Mr Ivanishvili took power in an uneasy cohabitation with President Saakashvili, whose term does not end until next year, a stream of arrests have targeted figures associated with the defeated party.