Trading standards in Nottinghamshire say the use of forged pet passports is on the increase as they seize one a month over the last year.
The team said the problem was leading to more illegally imported puppies in the UK and a heightened risk of rabies.
Pet passports were introduced nationally in 2012 and allow animals to travel freely between member countries.
Officer Paul Gretton said the problem of forgeries was almost non-existent three years ago.
“People are often tempted by cheaper pedigree dogs sold on the internet,” he said. “Unfortunately they are often from a dubious source.
“Owners are then faced with the agonising decision that it could cost hundreds and in some cases thousands of pounds in quarantine and veterinary bills – or face having their pet destroyed.”
Mr Gretton said dealers were forging passports and falsifying details to bring puppies into the UK when they were too young and without vaccinations. They are also often advertised online for half the price.