BEIJING (AP) -- Police barred artist Ai Weiwei from attending the hearing of a lawsuit his company brought against Beijing tax authorities and blocked filming at the courthouse Wednesday as part of an intimidation campaign against the outspoken government critic.

Ai told reporters that police the previous night had ordered him to stay home and steer clear of the courts. He said he agreed.

Chinese authorities detained Ai for three months last year and his design company was ordered to pay 15 million yuan ($2.4 million) in back taxes and fines, a penalty interpreted by activists as punishment for his criticism of the authoritarian government.

The company has appealed the fine and separately filed a lawsuit that accuses the tax bureau of violating laws in handling witnesses, evidence and company accounts in the case.

To the surprise of many, the lawsuit was accepted.

Ai‘s wife Lu Qing, who is the legal representative of his design company, Beijing Fake Cultural Development Ltd., went to the hearing with several lawyers and an accountant.

Plainclothes and uniformed police were stationed outside Ai’s home and studio in northeast Beijing on Wednesday, registering journalists who showed up to interview Ai and report on his case. Ai argued briefly with them and demanded to know why they were interrogating his visitors. Reporters were also blocked from filming at the courthouse.

Liu Xiaoyuan, a legal consultant who has been staying at Ai‘s home, was missing Wednesday after being taken away by police Tuesday night, Ai said.

Since he emerged from detention last year, Ai has been refused permission to travel and is under constant surveillance. He still frequently criticizes the government on Twitter, which is blocked in China but accessible to tech-savvy citizens.