The Australian Competition and Consumer Commission says it has received almost 4000 complaints in one month about the price of the COVID-19 home-testing kits and is investigating possible breaches of consumer law.

A $30 test should be considered "beyond outrageous" and $20 is also overpriced, ACCC Chair Rod Sims told reporters on Tuesday.

Complaints had recently been received about some BP branded petrol stations and IGA outlets.

"I'm hoping they send a message out to their chains to not engage in this excessive pricing," Mr Sims said.

"They may find some of their stores in court for unconscionable conduct, and that is a very, very bad look.

"We are trying to send a message out to head offices - if you have a store in your network that is doing the wrong thing, get them to stop it."

Retailers who had told customers that prices were high because of inflated wholesale costs could be investigated, he said, adding this was "not true".

Retailers claiming tests had been "commandeered by the government" - that's been denied by the Commonwealth - were also being investigated.

One party who made such claims had backtracked, he said.

Anyone who had said unverifiable things should withdraw them.

Most of the complaints about the cost of tests came from NSW, which Mr Sims said is likely due to the state's Omicron wave.

"But we are finding increasingly more reports from around the country."

The ACCC believes many individual stores are buying rapid tests from other retail shops and onselling them at an excessive mark up.

There have also been complaints of packet splitting, which is illegal.

These complaints have been referred to the Therapeutic Goods Administration and the Australian Federal Police.

Retailers will be investigated by the ACCC for whether they engaged in unconscionable conduct - a criminal offence which can lead to prosecution.

Price gouging of rapid tests is also an offence under the Biosecurity Act.

Up to 50 sellers of the tests, including major retailers and pharmacies chains, have now been asked to explain their costs and pricing.

The consumer watchdog says it has received close to 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.

Australian Associated Press