Mr Ai was released on bail last Wednesday. Chinese authorities said he confessed to tax evasion and pledged to repay the money owed. His family has denied he evaded any taxes and activists have denounced the accusation as a false premise for detaining Mr Ai, who spoke out against the authoritarian government and its repression of civil liberties.
The Beijing Local Taxation Bureau told Mr Ai he owed around $770,000 in unpaid taxes and would be fined about $1.1m, totalling just over $1.85m, Beijing human rights lawyer Liu Xiaoyuan said yesterday. Mr Liu does not legally represent Mr Ai, but has been a friend and supporter of the artist for many years.
Chinese authorities sometimes try to silence critics by accusing them of tax violations or other non-political crimes.
Mr Ai, whose work has been exhibited in London, New York and Berlin, has earned huge sums selling his work at auctions and through galleries.
Last year, he filled the Turbine Hall of London's Tate Modern with millions of handmade porcelain sunflower seeds. A 100kg pile of the seeds sold for more than $550,000 at a Sotheby's auction in February.
Mr Ai's mother, Gao Ying, said two tax bureau officials delivered the notice to Mr Ai on Monday and asked him to sign it in acknowledgement, but he refused. Ms Gao said she did not know all the details in the notice, but said the alleged violations took place over the past decade.
"We don't know anything about these taxes," she said. "These taxes date back ten years. Why, at that time, if they really had not paid their taxes, why did they not say anything about it every year?"
Mr Ai declined to comment, saying the terms of his bail barred him from giving interviews.
Ai Weiwei was the most high-profile target of the government's recent nationwide crackdown on bloggers, lawyers and activists aimed at derailing potential democratic uprisings like those sweeping through North Africa and the Arab world.Before he disappeared, Mr Ai had been keeping an informal tally of the recent detentions via micro-blogging website Twitter.
When he was released, the Chinese foreign ministry repeated allegations reported earlier by state media that a company linked to Mr Ai, Beijing Fake Cultural Development Ltd, had evaded a "huge amount" of taxes and intentionally destroyed accounting documents.
Previously, his wife, Lu Qing, said the company, which handles business aspects of Mr Ai's art career, belongs to her.
Ms Lu has said that Mr Ai is forbidden to discuss the conditions of his detention and release and is followed by plainclothes police officers whenever he leaves the house.
Mr Ai's detention prompted an international outcry among artists, politicians and rights activists, and Western leaders called it a sign of China's deteriorating human rights situation. His family and supporters say he is being punished for speaking out about the Communist leadership and social problems.
Mr Ai has spoken critically about a number of national scandals, including the deaths of students in shoddily built schools that collapsed during the 2008 Sichuan earthquake; children killed or sickened by tainted infant milk and a fire in a Shanghai high-rise building that killed 58 people. It was blamed on negligent workers and corrupt inspectors.
In previous cases involving economic crimes that others saw as political persecution, Zhao Yan, a news assistant for the New York Times, was jailed for three years in 2007 on charges of financial fraud. And Xu Zhiyong, an outspoken lawyer, was investigated for alleged tax evasion in 2009 but later released.
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