Thousands of Chinese added their contributions Tuesday to help artist Ai Weiwei pay a massive tax bill that many see as an attempt to silence the outspoken social critic.

A volunteer working at Ai's Beijing art studio said more than 20,000 contributions have now come in, both from China and around the world.

The volunteer said the contributions now total more than $900,000.

Ai, who was held without charges for almost three months earlier this year, has been ordered to pay $2.4 million in back taxes by next week.

Ai's supporters, however, suspect that the tax bill was manufactured to justify his detention for political reasons. Ai says the authorities have never explained to him the basis for the bill, and that they are still holding his accounting records.

The artist told Reuters news agency in an interview Tuesday that he has not yet decided whether to pay the bill.

He said if he pays, that will make it possible to appeal the bill. But he said police have told him that paying the bill would be taken as an admission of guilt. He has also been told if he doesn't pay, the affair will be treated as a criminal matter.

Ai's supporters in the international art community worry that the high-profile donation campaign may lead to more legal trouble for the artist. But Swiss art gallery owner Urs Meile, who works with Ai, says the man is driven by the same forces that made him China's most celebrated modern artist.

At Ai's studio in Beijing, volunteers acknowledge that the donation campaign has become more than just an attempt to help a wealthy artist with a tax bill.

Volunteer Zhang Haining says by making small contributions, the thousands of Chinese can forge a powerful and fearless political force.