Financial police in Belarus raided the editorial office of the largest independent online news site and the homes of several staff, and blocked its website.
The government had stripped Tut.By of its official media status in autumn as authorities cracked down on the largest street protests to erupt against longtime President Alexander Lukashenko in the post-Soviet republic's history.
The State Control Committee, to which the financial investigation department reports, said a criminal case against unnamed staff had been opened over suspected tax evasion.
Staff at Tut.By, which has covered the protests in detail, did not respond to telephone calls on Tuesday. Its front doors were locked.
The outlet said on its website that police officers were at its regional offices as well its office in the capital.
Tut.By's website was later unavailable. One of its founders said its domain had been blocked.
One of Tut.By's journalists, Yekaterina Borisevich, was sentenced to six months in jail in March after she challenged an official assertion that a protester who was killed had been drunk at the time of his death.
Around 35,000 people have been detained for taking part in street protests since they flared in August, human rights groups say. Dozens have received jail terms. Authorities say more than 1,000 criminal cases have been opened.
(Writing by Tom Balmforth; editing by Angus MacSwan)
