Northern Ireland motorists have been advised to carry an insurance document when crossing the border in the event of a no-deal Brexit.
In new guidance, the Association of British Insurers (ABI) said drivers should contact their insurer to arrange what is known as a green card.
It has warned that those who travel without one may be breaking the law.
The ABI warned that companies may apply a "small administrative charge" to issue green cards.
An agreement was reached between European insurance authorities in May to waive the need for green cards but this has not been confirmed by the European Commission.
The ABI said therefore the industry was "planning on the basis of green cards being required".
"Green cards would be required under EU regulations as proof of insurance if there was no deal," the organisation said.
"The documents are supplied by your insurer and customers are advised to contact their insurer about a month before they travel to get one."
It said that if people choose not to apply for a card, the only other legal option available would be to purchase insurance locally after crossing the border.
The ABI is the main trade body for the UK insurance industry.
It has more than 250 member companies, including most household names and specialist insurance providers.
Speaking in the Dáil (Irish parliament) on Thursday, the Irish foreign minister said that the green card system would also apply to Irish drivers travelling in Northern Ireland and the rest of the UK.
Simon Coveney said it was "an example of contingency planning".
"Cars and vehicles that are transiting back and forth across the border or going to the UK will need to be able to show that they have valid insurance if they are stopped in the other jurisdiction," he added.
"If they carry the green card, which will be available for them, then they will be covered in that regard."