The ACCC says it has been receiving a large number of complaints about the price of the COVID-19 tests and is investigating possible breaches of consumer law.
Some 50 sellers of the tests, including major retailers and pharmacies chains, have now been asked by the ACCC to explain their costs and pricing.
The retailers will also need to verify claims they made to consumers about why they were charged high prices.
Referrals have also been made to the Australian Federal Police and the Therapeutic Goods Administration after tip offs about alleged illegal re-selling and packet splitting, the ACCC said.
The consumer watchdog says it has received almost 3900 complaints between December 25 and January 26 – an average of 121 reports a day.
The most complaints relate to pharmacies – 1309, or about 34 per cent of the complaints.
This is followed by 781 from petrol stations, or 20 per cent, and 764 from convenience stores, tobacconists and supermarkets, another 20 per cent.
"Community concerns about sales practices for rapid antigen tests remain very high, for good reason," ACCC Chair Rod Sims said.
"We thank the consumers who have taken the time to pass on to us crucial information about what is happening in this market.
"These reports, and the public scrutiny, are helping to keep prices at lower levels than otherwise."