Aung San Suu Kyi, the Myanmar leader overthrown in a military coup two days ago, was on Wednesday charged with violating a trade rule, a party spokesman said.
A court "ordered her to be remanded in custody for 14 days from February 1 to 15, accusing her of violating an import/export law," National League for Democracy (NLD) spokesman Kyi Toe wrote on Facebook.
The violation is allegedly over illegally-imported radios.
Former president Win Myint has meanwhile been charged with violating the Natural Disaster Management Act, Kyi Toe added.
The military seized control of the country on Monday and detained Suu Kyi, the country's de-facto leader, as well as hundreds of other lawmakers.
It alleges widespread voter fraud in November's general election in which Suu Kyi's NLD secured 396 out of 476 seats up for grabs. This would have allowed her to helm her own government.
The military-backed Union Solidarity and Development Party won only 33 seats. The military, known as the Tatmadaw, is automatically allocated 25% of the seats in the combined houses under the 2008 Constitution that was drafted under a previous military government.
The results of the election were to be confirmed by parliament on Monday.
The newly-installed military government has said that fresh elections will be held at the end of the year-long state of emergency. It has said it will probe alleged fraud in last year's elections and prioritise the COVID-19 outbreak and the economy.
A statement issued Wednesday in the name of the executive members of Suu Kyi’s party said that authorities began raiding the party’s offices in Mandalay and other states and regions on Tuesday and seized documents and laptop computers.
The statement on Kyi Toe's Facebook page said locks were broken at several offices. It denounced the raids as illegal and demanded that they stop.
The NLD has called for non-violent resistance to the military takeover.
Western countries, including the EU, member states, the UK and US, have widely condemned the coup and demanded Suu Kyi’s immediate release.
But the United Nations' Security Council failed to agree on a joint statement at an emergency meeting on Tuesday over Chinese opposition.