Pets in Northern Ireland will need passports and vaccines to visit Britain from July.
Vets have said the demand for vaccines, including rabies, to comply with EU rules as part of the Northern Ireland protocol is unethical and unnecessary.
Ruth Anderson from Co Down and her terrier Rosie regularly cross the Irish Sea. Their journey will get more complicated, and expensive, from July.
Rosie will need a range of vaccinations, including rabies, and a pet passport to comply with EU animal health requirements.
While that will mean more cost, Ruth is more concerned about the implications of giving Rosie vaccinations she does not need.
"Lots of people, including myself, are very concerned from the welfare perspective, that all of a sudden, to travel across our own country, Kingdom, whatever you want to classify it, puts us in the realm of actually giving our dogs medication that is unnecessary," she explains.
Cats and ferrets must also be inoculated as they can also carry rabies.
Ruth's concern is shared by vets, who are opposed to the demand for vaccines they say are not needed.
"We understand the current bureaucratic and political needs, but the animal health and welfare need doesn’t exist," said Susan Cunningham, senior Vice President of the North of Ireland Veterinary Associstion.
"There’s a problem with any unnecessary procedure, a fundamental ethical problem with carrying out anything that doesn’t need to be done."
Susan owns three dogs and her adult children live in Scotland, so the new rules will have a personal, as well as professional, impact.
"There's no doubt that rabies is a horrific disease. I myself am a serial volunteer with mission rabies, vaccinating dogs all over the world, but there’s not currently a need here for such a vaccine."
Strictly speaking, pets in Northern Ireland require a passport and rabies vaccination to travel between Northern Ireland and the Republic.
That has been the case since both jurisdictions joined the European Union, but because there is no history of rabies on the island of Ireland, the regulations are not enforced and there are no border checks for pets.
Vets and pet owners in Northern Ireland hope an agreement can be reached to apply that North-South arrangement, to travel to and from Britain.
"We see no reason why the arrangement that has worked so well for many years between north and south should not also work east to west," Ms Cunningham said.
The British government has said it hopes to resolve the issue as part of ongoing discussions with the European Union about the implementation of the Northern Ireland protocol.