New rules have come in to effect to ensure the top five car rental companies in Europe fully comply with EU consumer law.
It follows the investigation of 49 complaints received by the European Consumer Centre Network in 2015.
These included hidden supplementary charges, allegations of damage to vehicles and additional costs imposed for fuel consumption.
Martina Nee of the European Consumer Centre in Dublin says the new changes should lead to better protection for consumers: "The European Consumer Network every year receives a lot of complaints in relation to car rental.
"The problem could be in relation to price increases, alleged damage to the vehicle or in relation to insurance cover or fuel policy.
"So hopefully this will lead to better monitoring and guidelines for the whole car rental sector and better consumer rights."