Police are carrying out random checks on cars in Cardiff, hoping to catch people travelling in from England for a spot of Black Friday shopping.
They will be able to stop any vehicle.
All but essential shops are currently shut under the lockdown in England. In Wales, rules have relaxed internally—but people are banned from crossing the border from England.
“The past few months have been difficult for us all, and with the rules having relaxed slightly, non-essential business reopening and Christmas just around the corner, it’s understandable that people will want to get out and about and enjoy all our city has to offer," Superintendent Jason Rees said.
“We are anticipating another busy weekend in our city centre, and while we will continue to adopt the policing style we have throughout the pandemic—working with the public to encourage voluntary compliance—we are committed to enforcing where blatant and flagrant breaches occur.”
Police say they will also be increasing patrols in the city centre "to encourage personal responsibility and to ensure compliance at pubs, bars, restaurants and hotels."
Anyone caught in breach of the rules will be fined "and given a direction to leave the city and return home."
Current rules in Wales limit social gatherings, with mass gatherings and house parties outlawed. Groups from four different households are allowed to meet indoors at pubs, cafes, and restaurants.
And while hospitality is currently shut down in England, in Wales pubs, bars and restaurants, gyms, and other businesses have opened their doors after the two-week firebreak lockdown.
Until Dec. 2 when the English lockdown ends, it is against the law to cross the border into Wales without a reasonable excuse, such as providing care or for work.
People can refuse to pay and to instead take the case to court, which can impose any fine in the case of a guilty verdict.
In addition to on-the-spot fines, according to the government, police have "wide-ranging powers to take practical steps to disperse gatherings, require people to go home and enter property."