Businesses that have reopened after months in lockdown have been warned about raising their prices.
The Competition and Consumer Protection Commission (CCPC) said firms must act individually when setting their prices and not collude by all raising them at the same time.
Among the groups that have been written to and warned about acting in concert to raise prices are hairdressers.
Both the Irish Hairdressers Federation and the Hairdressing Council of Ireland suggested that their members might be forced to introduce additional fees and hike prices.
The CCPC said it had been in contact with both hairdressing bodies to remind them of their obligations under competition law.
A number of service providers that have reopened this week said they may have to raise prices to meet social-distancing requirements.
The Hairdressing Council of Ireland had said many hair salons will introduce "Covid charges" or a small percentage increase costing between €5 and €10. And it warned of a rise in prices to cover the cost of personal protective equipment (PPE).
Peter Mark, which operates 69 stores in the Republic, caused outrage when it indicated it would be hiking prices by up to €60 in some cases to fix bad home dyes.
In a statement, the Hairdressing Council of Ireland said it had engaged constructively with the CCPC in the past few days.
"While the Irish Hairdressers Federation has issued strict and extensive guidelines on reopening safely, it is not our role to make any recommendations on prices as this is a matter for each individual salon owner to decide," it said.
The CCPC, which is the State competition enforcer, said it had been in contact with a number of trade bodies after they made public statements about new potential charges and price increases which their members may apply.
Service providers were told they must act independently in their commercial decisions, particularly when setting prices and charges.
Businesses have responsibilities under consumer protection law when setting new or additional fees, or making changes to business practices.
The CCPC said firms were free to introduce higher charges to meet public health requirements.
But they "must make such decisions independently and advise consumers of these costs before they make a purchase".
The competition authority said trade associations were free to advise their members on how to address the challenges they were facing.
"However, the practice of trade associations suggesting future prices, or co-ordinating ways of passing on costs to consumers, could constitute an infringement of competition law," it added.
CCPC chair Isolde Goggin said her organisation was acutely aware of the new challenges that businesses across the country were facing.
But she said they must be mindful that competition law rules remain unchanged.