The SPCA in Ireland says up to 1000 dogs are being trafficked into Britain each week from unlicensed Irish puppy farms.
The animal welfare charity told the BBC that huge numbers of puppies were being bred illegally in Ireland specifically for the British market.
Many dogs are bred in conditions that fail basic welfare standards and are infected with parasites and disease.
In October, 36 puppies packed into cardboard boxes were found in the back of two vans in Dublin - they had mange, ear mites, fleas, eye infections and parasitic infections.
Two days later, another 56 puppies were seized by police at Dublin Port and a further 26 dogs were discovered in the back of a horse box in Tipperary.
"There's no doubt that a large number of them are being trafficked out of the country every week through the Irish ports," ISPCA chief inspector Conor Dowling told the BBC.
Importing puppies to Britain is legal if the correct paperwork is in place and welfare standards are met.
New rules not followed
Irish controls were tightened last July, but the ISPCA and another animal charity, the Dogs Trust, say some breeders are not complying with the new rules.
Under a new act, anyone who owns six or more breeding female dogs over the age of six months must have a licence.
Since the Dog Breeding Establishments Act came into force, 120 dog breeding establishments have applied for registration and only 42 have been officially registered. The BBC says this includes boarding kennels and animal shelters.
Once in Britain, the puppies are sold to rogue dealers who hide their true health and origin.
The RSPCA said 87 puppies were discovered in raids in Stockport and Greater Manchester earlier this week.
Some dogs can fetch up to £1000 RSPCA chief inspector Ian Briggs told the BBC.