Ireland could be seen as an easier route in for holders of less secure EU passports, the UK’s immigration minister said.
Greek and Italian passport users don’t have biometric data included and one MP warned of loopholes and security lapses.
Northern Ireland’s land border with the Republic is one of the most vexed issues facing the Brexit negotiators.
Minister Caroline Nokes said the issue of biometric passports would be raised with the EU.
She added: “There are some nationalities who use identity cards which are far less secure than biometric passports and I have concerns that moving forward, as we move into a new immigration system post-Brexit, that we will get to a position where we will no longer accept those.
“That is some five years after exit, after our negotiations with the EU, but obviously those are conversations that will be ongoing with members of the EU, but particularly with Ireland.
“I am very conscious that that could potentially be seen as an easier route in because Ireland will be obliged to accept the less secure travel documents that some of the EU-27 still enable their citizens to use.”
She addressed the Northern Ireland Affairs Committee of MPs at Westminster.
Conservative committee member Robert Goodwill said: “There are loopholes and security lapses with Greek and Italian identity passports which are not biometric, obtained from the town hall.”
All Irish passports have been biometric since 2006.
Ireland’s major point of entry is Dublin airport. In 2016 immigration services there processed nearly 14 million passengers.
Ireland has been implementing an EU directive on passenger name records which is intended to help prevent terrorism.
It has a system to enhance identity document checks as part of the citizenship process which has resulted in the earlier detection of fraudulent claims, an annual review from the Irish Naturalisation and Immigration Service said.
Self-service e-Gates introduced at Dublin Airport last year automate routine immigration checks for EU passengers and provide new channels to pass through the immigration process, the review added.
They were designed to allow passport control staff to assign additional time to more complex cases and identify cases of potential abuse at the border.