A restriction on using public transport for essential use is formally removed from Monday.
It was imposed during the height of the coronavirus restrictions when bus and trains were used mainly by key workers and those unable to work from home.
The Welsh Government said the change was part of a phased approach to easing restrictions.
Wearing face masks is compulsory on public transport in Wales, but there are exemptions on health grounds.
Cardiff Bus said it has added extra journeys to some of its services as "demand has increased", with additional safety measures introduced.
Transport for Wales said it has increased safety measures on trains and buses and has also made stations one-way for passengers.
Chief executive James Price said: "I'd like to reinforce the message that it is now mandatory to wear face coverings on public transport and those failing to comply with the rules, who are not exempt, will be refused travel and could be fined by the British Transport Police.
"These measures are to ensure the safety of other customers and our colleagues and we expect people to take personal responsibility to comply."
Lee Waters, Deputy Minister for Economy and Transport, said: "It's essential that people act responsibility when using public transport" as the virus was still in circulation.
"This will involve planning journeys to avoid busy periods if possible, and washing or sanitising hands at the start and end of each trip," he said.