Revenue officers at Dublin Port took have taken custody of a puppy.
They stopped and questioned a couple who were travelling to the UK on Wednesday afternoon.
Officers say the couple did not have a pet passport for the puppy, nor was it microchipped or vaccinated.
This is required under the Animal Health and Welfare Act 2013.
The female Jack Russell puppy was transferred into the care of the DSPCA, where she is receiving veterinary attention.
Revenue say it collaborates closely with the DSPCA and other agencies to combat the illegal trade in puppies.
A follow-up investigation is in progress.