They are charged with illegal assembly and damaging property.
Thirty-eight members of Tanzania's main opposition party, including two lawmakers, have been in custody for a week following local elections, their lawyer said Wednesday.
MPs Susan Kiwanga and Peter Lijualikali, as well as 36 other members of the CHADEMA party, were arrested on November 29 in Morogoro, 200 kilometres (120 miles) west of Dar es Salaam.
They are charged with illegal assembly and damaging property, while the two MPs also face an extra charge of incitement to violence. All deny the charges.
"This is a purely political case," their lawyer Peter Kibatala said. "They plead not guilty."
The CHADEMA party said their members were arrested after they challenged election results won by the ruling party of President John Magufuli. They accuse the justice system of not being independent.