Officers in the Welsh capital have been given the power to arrest and amend drivers from 9 a.m. on Friday in a bid to prevent people from outside the country from reaching its capital.
South Wales Police said they distributed 12 fixed penalty notices on the first day and warned 15 other people, ordering them to leave Cardiff.
People from high risk areas outside of Wales are not allowed to enter the country under Welsh government rules.
Among those breaking the law were a couple from Essex who told officers they were traveling to Cardiff to give Christmas presents to the family, and a group of nine traveling in convoy to visit friends at university.
Cardiff and Vale of Glamorgan Chief Superintendent Wendy Gunney said: “I want to thank the vast majority of people who are enjoying their weekends cautiously and within the bounds of existing regulations, but those who do. no rules continue to put others at increased risk.
“The measures that are in place are in place for a reason. Our checks will continue throughout the weekend, and anyone who blatantly breaks the rules, which have been very clear, faces a fine.
Police have been given temporary additional powers over concerns that groups of people from locked areas of the UK where pubs and bars are closed helped pack the streets of Cardiff city center over the past weekend .
South Wales Police have said in addition to vehicle checks they have more officers on duty, and these changes will be in place until 5 p.m. Sunday – covering the last weekend of the lockdown of England.