US Fed Chairman Alan Greenspan and Treasury Secretary John Snow on Thursday warned Congress against imposing major tariff hikes on Chinese imports in order to pressure Beijing to revalue the renminbi, the Asian Wall Street Journal reported. Both men, citing proposed punitive legislation, said that increasing tariffs would not solve the problem of the US trade deficit and would harm the US economy and living standards. They urged a revaluation of the renminbi but said financial markets should be allowed to operate without interference.