The Senate tax-cut bill differs from one in the House of Representatives and could complicate a Republican tax overhaul push, increasing skepticism on Wall Street about the effort.
The dollar was 0.32 percent lower against the Japanese currency to 113.49 yen. It fell to a low of 113.86 yen, its lowest since Oct. 31, earlier in the session.
The dollar index <.DXY>, which tracks the greenback against six major currencies, was down 0.22 percent at 94.656.
"There is something of a risk-off undertone that may prevail in the market until we get some clarification on the tax cut plan we are expecting to get from the Senate," said Shaun Osborne, currency strategist at Scotia Bank in Toronto.
Any potential delay in the implementation of tax cuts, or the possibility of proposed reforms being watered down, would tend to work against the dollar, analysts said.
Traders also pointed to a sudden fall in Japanese equities from multi-decade peaks on dampening risk sentiment in Asian trade, a mood that continued into London trading hours with European stocks also falling.
The dollar index was little changed after data showed the number of Americans filing for unemployment benefits rose more than expected last week, suggesting that claims processing disrupted by recent hurricanes has begun to improve.
"Essentially they are still at extremely positive levels," said Osborne.
"We know we have a very tight labor market in the U.S. but that’s not yet translating to significantly higher wages. That's still the caveat to the labor market story."
Euro zone government bond yields jumped on Thursday, kicking recent sharp falls into reverse, and the euro climbed to a six-day high. The common currency was up 0.3 percent against the greenback.
Britain's sterling was little changed on the day as expectations for a gradual tightening of policy from the Bank of England protected the pound from the political turmoil engulfing Prime Minister Theresa May's government.
(Reporting by Saqib Iqbal Ahmed; Editing by Susan Thomas)
By Saqib Iqbal Ahmed