Artist and dissident Ai Weiwei said Tuesday Chinese authorities had threatened to refer his case to police if he did not meet a looming deadline to pay a 15 million yuan ($2.4 million) tax bill. Ai was given until Wednesday to settle a bill for back taxes levied against a company he has links to, after he was released earlier this year from 81 days in police detention. The artist maintains the government's charge that he evaded taxes for years is politically motivated, and has said he will challenge it using money donated by supporters as the collateral needed to lodge an appeal. But on Tuesday, Ai said tax officials had rejected his offer to put up 8.5 million yuan in collateral against the tax evasion charge and were threatening to "kick the ball to the police" if the issue was not settled. Ai said the situation was uncertain, but it appears the authorities were not satisfied with his proposal to provide evidence that he has the money in a bank account and wanted it instead to be paid directly to them. "They are discussing putting the money directly into their account, but it's all very bureaucratic and not at all certain what will happen next," Ai told AFP. "They threatened to kick the ball to police." The artist, best known for his role in designing Beijing's "Bird's Nest" Olympic stadium, has denied any wrongdoing and insists the government is trying to silence him and his vocal human rights activism. Over the past week, some 30,000 supporters have donated money through Internet and bank transfers, while some even threw cash over the walls into his courtyard home, including banknotes folded into paper planes. Total donations had reached 8.69 million yuan by Sunday night, when the appeal closed, according to Ai. His case is particularly complicated because the tax bill was levied against Beijing Fake Cultural Development, a company he founded but which is owned by his wife. He has said he will pay back his supporters once the case is over, and does not want to hand over the money raised to Chinese authorities for fear that it will not be returned to him. "The lawmakers can interpret the case however they like because no (Chinese) media is allowed to write about the case," he said.