The consumer watchdog is "significantly concerned" about the increasing prices of COVID-19 rapid antigen tests.
The Australian Competition and Consumer Commission said at the "extreme end" it had received reports of RATs costing up to $500 for two tests through online marketplaces, and more than $70 per test through convenience stores, service stations and independent supermarkets.
Despite wholesale RAT costs being up to $11.45 a test, the ACCC said prices for the at-home kits were often retailing between $20-30 per test, and were priced much higher through smaller outlets.
ACCC chair Rod Sims described some of the recent retail mark-ups as "clearly outrageous".
"There are several businesses that have repeatedly come to our notice thanks to the information provided by the public. We are asking those businesses to urgently explain the prices they are charging," Mr Sims said in a statement on Monday.
He said the "concerning practices" had come to light from the ACCC's analysis of more than 1800 reports from the public since Christmas.
The agency is receiving close to 150 reports per day from concerned members of the public about RAT pricing, he added.
Chemists are the traders most commonly reported, followed by convenience stores, tobacconists, supermarkets and petrol stations.
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"We are looking in particular at reports of single tests being sold at around $30 or above from certain stores. For example, such sales have occurred from a number of King of the Pack and Metro Petroleum stores," Mr Sims said.
"The complaints are limited to a small number of individual stores in these chains and the majority of stores in those chains have not been the subject of complaints to us.
"We are writing to those traders to validate the reports and asking them to explain their prices so we can work out what's going on."
Other concerns are retailers failing to provide receipts, unscrupulous selling on online marketplaces, and reselling and repackaging of the at-home tests.
Mr Sims said the ACCC had contacted more than 40 test suppliers, major retailers and pharmacy chains across the country reminding them they need to back up claims to consumers about reasons for higher prices.
"We will continue our investigations and analysis of information from consumers, retailers and suppliers, and will provide further updates in coming weeks," Mr Sims said.
Australian Associated Press