The design firm of Chinese government critic Ai Weiwei is challenging a $1.85 million tax bill presented by authorities to the acclaimed artist and activist just days after he was released from nearly three months of confinement.

A lawyer retained by Ai's company said he filed an appeal Wednesday asking for an administrative review of the bill with Beijing's local tax bureau. The lawyer, Pu Zhiqiang, said the appeal comes from Ai's wife, Lu Qing, who is listed as the legal representative of her husband's company. It was not immediately clear if or when a ruling will be issued.

Ai's mother said authorities delivered the delinquent tax notice to her son Monday and that he refused to sign documents acknowledging the debt.

Chinese authorities say Ai confessed to tax evasion during his confinement, which began with his arrest in early April in Beijing. But his family denies he evaded taxes, and supporters claim he was arrested for his outspoken criticism of Beijing's ongoing crackdown on civil liberties.

Ai was arrested April 3, at the height of a Chinese crackdown on dozens of lawyers, dissidents and human rights activists. Weeks after the arrest, authorities announced Ai's tax evasion charges.

Critics have described the government crackdown as a thinly-veiled attempt to stifle public protests like those in the Middle East and North Africa earlier this year. Ai's arrest sparked protests at art venues in a host of Western countries and has been widely criticized by the United Sates and other Western governments.