Police will step up patrols on trains this weekend as Cardiff prepares to be hit by hundreds of Black Friday shoppers and rugby fans.
Transport for Wales (TFW) will also be using extra staff across its network after more than 2,000 people had to be asked to wear a face mask last weekend.
TFW also said getting on for 200 people were refused travel by TFW staff for not wearing a face covering, because of anti-social behaviour, or for being unfit to travel.
Last weekend, Cardiff was described as “crazy” with people believed to have come from England to visit the city.
England remains in lockdown until December 2, and under rules in both the UK and under Welsh legislation, people are not permitted to travel to Wales from locked-down areas for non-essential reasons.
Police in the city are anticipating another busy weekend as shoppers visit the town to catch Black Friday deals and Wales prepare to play England at rugby, with fans flocking to pubs to watch the game.
The rail network is also anticipating a busy Friday and weekend for the same reasons.
Find out about traffic and travel updates in your area:
TFW is encouraging people to plan ahead and also take advantage of its newly-launched capacity tracker to avoid busy periods.
Leyton Powell, TFW safety and assurance director, said they had seen footfall increase on trains since Wales left its fire-break lockdown.
He said: “As passenger numbers have grown in recent weeks, unfortunately we’ve also seen a small rise in anti-social behaviour and people failing to comply with the rules around face coverings.
“We want to reassure our customers we have deployed extra staff on trains and stations, especially on weekends, helping to keep everyone using our network safe.
“As we enter the Christmas period we are introducing even further measures to help people who may be unable to travel as a result of excess alcohol. This includes respite for vulnerable people, staff able to offer water and the use of rest areas until they are safe to travel.”
British Transport Police Chief Inspector Jon Cooze added: “Our officers and PCSOs will continue patrolling the rail network, supporting rail staff in engaging with passengers about the importance of maintaining social distancing, and reminding those who are travelling to wear face coverings.
“We urge the public to continue to act responsibly and play their part in helping to protect themselves, and each other, by following the guidance and restrictions set out by the Government, as well as complying with the requirement to wear face coverings.”