The US House of Representatives initially passed the tax legislation in a Tuesday afternoon vote, but the bill included provisions that did not comply with Senate rules.
The Senate was expected to vote on a revised version of the bill, with the offending provisions removed. If the Senate approves the bill as expected, the House will vote again on Wednesday.
The bill, which includes generous tax cuts for big businesses, had buoyed US stocks ahead of the vote, but modest selling started once traders saw the bill's likely benefits as fully priced in.
The benchmark S&P/ASX 200 index was down 2.2 points at 6074 by 0117 GMT. It rose 0.5 percent on Tuesday, scaling a near 10-year high.
"Given the negative leads we have seen from overseas markets it's no surprise that we are seeing some pressure in the opening hour of trading," said Michael McCarthy, chief market strategist at CMC Markets.
Real estate, alongside healthcare, was the biggest decliners on the main board with retail property manager Scentre Group losing 0.7 percent.
Healthcare giant CSL Ltd lost 0.8 percent and was one of the biggest drags on the benchmark. A 1.2 percent decline for toll road operator Transurban Groups loss was a blow to the industrials sector.
"However, there is some optimism that underlying strength in the market might prevail over the course of the day," said CMC Markets' McCarthy.
Materials stocks partially offset losses elsewhere with global miners Rio Tinto and BHP Billiton gaining 0.1 percent and 0.8 percent respectively.
Shares of miners were underpinned by strength in commodity prices over last week, with iron ore prices pausing after strong gains.
Base metal prices were also upbeat overnight, before easing on Wednesday.
Theme park operator Ardent Leisure Group was the top gainer on the index, jumping 7.5 percent after selling its bowling and entertainment division for A$160 mln.
Shares of mining contractor Downer EDI Ltd rose 1.8 percent after news that it secured a mining services contract at the Gruyere Gold Project worth about A$400 million.
New Zealand's benchmark S&P/NZX 50 index hit its third record high in four consecutive sessions and was 0.1 percent higher at 8409, helped by healthcare and utilities shares.
Ryman Healthcare Ltd added 1.9 percent and was the biggest boost to the benchmark while power supplier Contact Energy Ltd followed suit, rising 0.9 percent.
Dairy products maker Synlait Milk Ltd tracked up 4.63 percent and was the index's top gainer after it said it intends to invest about NZ$125 million ($87 million) in a liquid dairy packaging facility to supply retailer Foodstuffs South Island.
Investors seemed to shrug off the country's quarterly current account deficit which came in wider than had been expected.