Motoring groups fear holidaymakers will face car-hire confusion following today's abolition of the paper part of the driving licence.
The paper counterpart shows a driver's record, including offences and endorsements, and is being replaced by an online service.
Drivers needing to show their driving record to car hire companies will need to have viewed their licence information online and to have generated a check code so details can be shared with third parties.
The Driver and Vehicle Licensing Agency (DVLA) said car rental companies in the UK and abroad would be well aware of the changes.
However, the AA said there was "widespread confusion as to what drivers now needed to do to stay within the law" while the Institute of Advanced Motorists (IAM) said drivers could be "caught unawares".
Also, recovery service GEM Motoring Assist warned there could be long queues at overseas' car hire offices while a survey by money.co.uk showed that as many as 79% of people could arrive at a car hire office with incorrect documents.
Transport Minister Lord Ahmad said said replacing the paper counterpart with an online service "will save motorists money and reduce unnecessary red tape".
He went on: "It will also benefit employers and vehicle hire companies. Relying on the counterpart meant relying on a potentially out of date piece of paper.
"Now, when the driver chooses to share it, those organisations will be able to see completely accurate information direct from DVLA's records. This will reduce their risk and improve road safety."
A DVLA spokesman said: "Hire companies in the UK, and through them their overseas offices, should be well aware of the change. Many have published information for customers on their websites as their own requirements vary.
"Our advice to drivers is to check with their hire company what documents or information they will be asking for. Drivers can generate a check code up to 72 hours before collecting the vehicle and if they want extra assurance they can also download or print out an electronic summary of their driving licence record."
An AA/Populus poll showed that a third of drivers who had hired a car abroad in the past five years had been asked to show their paper counterpart. The AA said that those hiring vehicles overseas from today should keep their counterpart as a "belt and braces" measure.
AA president Edmund King said: "The possibility of teething problems this summer is a concern.
"While most drivers will be happy to see the back of the counterpart, there is widespread confusion as to what they should now do to ensure they stay within the law and what documentation will be required at the rental check-in desk."
IAM chief executive Sarah Sillars said: "People are not aware of how many of the current procedures are changing."
GEM chief executive David Williams said: "We predict long car hire delays, particularly at overseas holiday destinations, simply because many car hire firms are going to be unaware of the changes."
Money.co.uk editor in chief Hannah Maundrell said: "We appreciate the DVLA's changes set out to make life simpler for drivers but teething problems are inevitable."
RAC Foundation spokesman Philip Gomm said: "Not many drivers will miss the dreaded paper counterpart.
"However the point of scrapping the paper section is to make motorists' lives easier. It would be a shame if the new online method of sharing endorsement details actually complicates things rather than simplifies them."
The Freight Transport Association (FTA) said it feared the new system would be more cumbersome for employers.
FTA spokesman Ian Gallagher said: "FTA members who employ hundreds if not thousands of drivers have complained to us that the proposed system adds time to the licence-checking process, forcing many to look for a cost alternative.''