Police stopped 110 drivers during the first 24 hours of random checks in Cardiff.
Officers in the Welsh capital were given the authority to stop and fine drivers from 9am on Friday in an attempt to prevent people from outside the country from traveling to the capital.
South Wales Police said they had issued 12 fixed criminal reports on the first day and warned a further 15 people by instructing them to leave Cardiff.
People from risk areas outside Wales are not allowed to enter the country under the rules of the Welsh government.
Those breaking the law included a couple who came from Essex and told the officers that they were going to Cardiff to give Christmas presents for the family, and a group of nine people traveling in convoy to visit friends at university .
Cardiff and Vale of Glamorgan Chief Superintendent Wendy Gunney said: “I would like to thank the vast majority of people who enjoy their weekend gently and within the bounds of existing regulations, but those who don’t follow the rules remain others with a increased risk.
“The measures that exist are there for a reason. Our checks will continue throughout the weekend and anyone who blatantly disregards the rules, which have been made very clear, could be fined. “
Police were given the temporary extra powers after concerns that groups of people from gated parts of the UK where pubs and bars have closed have helped pack the streets of Cardiff city center over the weekend.
South Wales Police said they have employed more officers in addition to vehicle checks, and these changes will be in effect until 5pm Sunday – the last weekend of the England lockdown.