The consumer protection watchdog says fuel companies are not obliged to pass on cuts in excise duty.
A number of TDs have called on the Competition and Consumer Protection Commission (CCPC) to investigate, after petrol stations hiked prices in advance of an excise cut from the Government.
However the CCPC says it has no control over prices charged.
"The CCPC is not a price regulator and does not have a role in monitoring price levels across the economy", it says.
"As businesses in Ireland have the power to decide how much they will charge consumers for products, this means that the CCPC does not have a role in reviewing or approving price increases."
It says it can investigate "in very specific circumstances" and refer a case for criminal prosecution where businesses form a cartel and collude to fix prices.
But it explains: "In rare situations, where there is a dominant supplier of a good or service, there may be circumstances where a trader is considered to be in breach of competition law by charging excessive prices.
"These are a very specific scenarios and cases of this type are rare across Europe", it adds.
While the Irish Road Haulage Association says talks are ongoing to secure more relief for truck drivers over high fuel costs.
President of the orgainsation, Eugene Drennan, told The Hard Shoulder he is more positive that a resolution can be found - and the need for a protest could be avoided.
"We still need to go to our customers, hauliers have to go to customers because the fuel is so high now.
"We were disappointed with just a 12.5c [reduction] because we put six different scenarios to Minister Ryan six weeks ago.
"And then we went on to Minister Donohoe to plead our case and put scenarios to him."
Mr Drennan says the result they got "didn't hit the mark for us".
"And we went to the Minister last night and put different scenarios to him again, and we're working with him all day today.
"It is not finalised yet, we're still working."
'An extra bit of relief'
Mr Drennan says talks are ongoing, and that is a good thing.
"You still have to go to your customers, you have to get an increase, you will have to get a surcharge.
"But also we are working to, and still in talks, to get an extra bit of relief.
"And that's ongoing - and just to say, I would be a little more relieved this evening than I was on Wednesday evening or Tuesday".
Transport Minister Eamon Ryan told Newstalk on Wednesday the Government will be looking at more measures over the next few weeks.
"We'll be coming back in a number of weeks' time, particularly looking at a number of efficiency or other measures that can help people save money in other ways.
"We're going to have to continue to respond in an increasingly flexible way.
"I think the focus will switch towards efficiency, because the international prices are outside our control".
And he said more will have to be done to help those operating in the school transport and haulage sectors.
"I think it's really important that the haulage industry which is badly affected, badly exposed... where they're tied into a contract, or where their customers are not allowing them pass on the cost, that is one of the areas we will have to look [at].
"In those sort of areas where a public service can't be provided because that long-term contract is not reflecting some of the prices, we will in certain targeted areas have to adjust and amend", he added.
Additional reporting: Sean Defoe