Just after noon AEDT on Tuesday, the benchmark S&P/ASX200 index was down 66.9 points, or 0.81 per cent, to 8,241.3, while the broader All Ordinaries had fallen 69.4 points, or 0.81 per cent, to 8,490.7.
US President Trump told reporters overnight that his 25 per cent tariffs on Mexico and Canada would come into effect next week once a month-long delay on their implementation expires.
"We're on time with the tariffs, and it seems like that's moving along very rapidly," Mr Trump said at a White House press conference with French President Emmanuel Macron.
He stressed more broadly that US "reciprocal" tariffs were on schedule to begin as soon as April.
Eight of the ASX's 11 sectors were lower at midday, with energy, consumer staples and utilities higher.
The consumer discretionary sector was down 2.3 per cent as Domino's Pizza Enterprises plunged 10.9 per cent after announcing its half-year earnings, while Guzman Y Gomez had dropped 4.5 per cent and Wesfarmers had fallen 2.9 per cent.
In the material sector, Johns Lyng Group had plummeted 29.1 per cent to a nearly five-year low of $2.695 after the building clean up company said its net profit for the first-half had dropped by a third, to $20.8 million.
It had been a challenging operating environment, Johns Lyng said, with benign weather conditions across Australia resulting in a reduced volume of insurance claims.
In the heavyweight mining sector, BHP was down 1.1 per cent, Fortescue had dropped 3.0 per cent and Rio Tinto had dipped 0.9 per cent.
All of the big four banks were lower, with ANZ dropping 1.2 per cent, NAB retreating 2.0 per cent, Westpac dipping 0.5 per cent and CBA falling 1.8 per cent.
In currency, the Australian dollar was buying 63.42 US cents, from 63.77 US cents at 5pm AEDT on Monday.
