Zambia's main opposition leader Hakainde Hichilema has been charged with treason after allegedly obstructing the presidential motorcade.
Mr Hichilema's convoy allegedly refused to make way for President Edgar Lungu's convoy on Sunday, while travelling to a ceremony.
A confrontation erupted between the two convoys, as the president's motorcade attempted to overtake Mr Hichilema's.
Neither Mr Hichilema nor his lawyer has commented since he was charged.
Police said Mr Hichilema's convoy endangered the president's life.
Treason is a non-bailable offence in Zambia, with a minimum jail term of 15 years and a maximum sentence of death.
Mr Hichilema was arrested on Tuesday after armed policemen raided his home in an affluent suburb in the capital, Lusaka.
He accused police of firing tear gas into his home while his wife, Mutinta Hichilema, said they "wanted to kill my husband".
Last year, Mr Lungu narrowly beat Mr Hichilema in presidential elections.
Mr Hichilema's United Party for National Development (UNPD) says it does not recognise Mr Lungu as president. It alleges the poll was rigged.
He has been charged with five of his aides, following the battle of the motorcades on the road between Limulunga and Mongus, some 500km (300 miles) west of Lusaka.
"The opposition leader disobeyed police orders to give way to the presidential motorcade in an attempt to put the life of the republican president in danger," police chief Kakoma Kanganja told reporters.
Mr Hichilema and his aides have also been charged with using insulting language, he added.
Mr Hichilema is already facing charges of sedition dating from last October, a move his party said was an attempt by the ruling party to silence dissent.
He was out on the bail when he was arrested on Tuesday.