The S&P/ASX200 fell 31 points on Monday, down 0.33 per cent to 9,232.6, as the broader All Ordinaries lost 21.1 points, or 0.22 per cent, to 9,424.
Westpac tumbled more than five per cent after its third-quarter mortgage applications slumped by a fifth following May's federal budget announcement, raising concerns about how banks would fare this earnings season.
Traders had been bracing for budget-related volatility to hit the market, likely starting with the banks, IG market analyst Tony Sycamore said.
"Impacts on property prices, credit growth and removing investors from the market, that's going to flow through to the banks," Mr Sycamore told AAP.
Miners offered a ballast to the financial sector weakness as gold and lithium prices advanced, while BHP and Rio also made gains despite Friday's sharp pullback in copper prices.
Energy stocks ended the day flat as oil prices eased after spiking, with a deal to reopen the Strait of Hormuz remaining elusive.
Uranium and coal stocks outperformed the sector though, with Paladin and Bannerman Energy up more than two and four per cent respectively.
The communications and health care sectors made solid gains, each up 1.5 per cent or more, with strong performances from ResMed and Seek, while Car Group's value soared 10 per cent after a stellar full-year profit.
In company news, Penfolds owner Treasury Wine Estates has flagged $558.4 million in writedowns and impairments as it looks to streamline its US supply chain.
After a months-long bidding war, I Squared Capital will buy oOh! Media in a $1 billion deal after edging out suitors including Oaktree Capital and Pacific Equity Partners.
Tabcorp shares improved after the company confirmed it would buy wagering technology provider BetMakers for $267 million.
The Australian dollar is buying 70.66 US cents, up from 70.33 US cents on Friday at 5pm AEST, holding at multi-week highs ahead of the Reserve Bank's interest rate decision on Tuesday.
Earnings season continues with SGH, Southern Cross Media and Life360 to hand down results on Tuesday ahead of CommBank, AGL and Suncorp on Wednesday.
After outperforming its global peers in July, the ASX200's shaky start to the week potentially pointed to recent investor complacency, Global X ETFs senior strategist Marc Jocum said.
"With the RBA decision due tomorrow and Commonwealth Bank next on the reporting season chopping block ... investors may be about to discover whether Westpac was a one-off setback or the opening crack in the dam wall, with the first domino now fallen," Mr Jocum said.
ON THE ASX:
* The S&P/ASX200 fell by 31 points, or 0.33 per cent, to 9,232.6
* The broader All Ordinaries lost 21.1 points, or 0.22 per cent, to 9,424
One Australian dollar trades for:
* 70.66 US cents, from 70.33 US cents at 5pm AEST on FridayÂ
* 111.92 Japanese yen, from 111.37 Japanese yen
* 61.16 euro cents, from 61.04 euro cents
* 52.36 British pence, from 52.28 pence
* 120.01 NZ cents, from 119.90 NZ cents
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