BEIJING (REUTERS).- Chinese authorities are setting hurdles for artist-activist Ai Weiwei to pay a bond that would let him appeal a tax fine his backers have called a political vendetta, threatening to complicate his legal battle, one of his lawyers said Monday. Ai, whose secretive 81-day detention this year sparked worldwide attention, has until Wednesday to lodge collateral that would allow him to contest a 15 million yuan ($2.4 million) fine for tax evasion, which he denies. But the government is demanding he pay the 8.4 million yuan bond in cash straight into a tax bureau bank account, something his lawyer Pu Zhiqiang said lacked legal provision. The government is also refusing to accept Ai’s mother’s house as collateral, Pu added. “We have done everything we were