The consumer watchdog has launched court action against supermarket giants Coles and Woolworths over their fuel shopper docket schemes.

The Australian Competition and Consumer Commission (ACCC) has instituted proceedings in the Federal Court for allegedly breaching undertakings made by the companies.

ACCC chairman Rod Sims says Coles and Woolworths agreed in December last year to limit fuel discount vouchers to a maximum of four cents per litre.

The limit on discounting was meant to take effect from January 1.

"The ACCC takes alleged breaches of undertakings extremely seriously. Such undertakings are generally accepted by the ACCC as an alternative to the ACCC taking court enforcement action," Mr Sims said.

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"We think it affects the long-term health of the petrol market and actually we think it affects how much people are paying for petrol right now at the bowser.

"If you've got these discounts then, yes, we accept that you're getting a benefit. If you don't have the discounts then we're concerned you're paying too much for fuel."

The commission says Woolworths is currently offering a bundled discount of up to eight cents per litre, while Coles is offering a discount of as much as 14 cents per litre.

The discounts are only available to customers who made qualifying purchases at Woolworths or Coles supermarkets.

Consumers who spend $30 at the supermarkets receive a four cent discount, which is increased if they then spend additional money at the Woolworths or Coles petrol station.

A directions hearing for the case is scheduled to be held at the Federal Court in Sydney on April 3.

The ACCC has been investigating discount shopper dockets since 2012.

Mr Sims confirmed his concerns about fuel discounts in July last year, saying he believed they could lead to higher fuel prices in the longer term.

"If these shopper dockets continue at these levels, it's going to be very hard for other players to compete and we may end up with just two companies in the country selling petrol," he said at the time.

Coles, Woolworths respond to ACCC claims

Coles has provided the ABC with a short statement, implying it has a different interpretation of the agreement it reached with the ACCC last year.

"We welcome the opportunity to clarify conflicting interpretations of the voluntary undertaking on fuel discount dockets in court," the company said in a statement.

Woolworths has also released a statement, saying it is considering changes to its discount scheme.

"We remain disappointed that we have been curtailed from offering greater petrol discounts to our customers," Woolworths said in its statement.

"We have discussed with the ACCC making our discounts independent of each other and this change is underway.

"We believe our undertaking with the ACCC allows customers to combine offers of four cents from the supermarket and four cents from the petrol store to receive eight cents a litre off their fuel.

"The ACCC has expressed a view that customers should only have access to one 4 cents offer at a time.

"Yesterday Woolworths asked the Court to make a declaration that allowing customers to redeem both discounts at the same time is in accordance with the undertaking."