ScotRail estimates around 40% of customers travelling on trains in Fife aren't covering their face.
That's despite face coverings being mandatory on public transport.
The new rule came into force last month, although there are some exemptions, for example children under 5-year-old.
The Scottish Government's website also states there may be a reasonable excuse for someone not to wear one if they have a health condition or disability and using a face covering causes difficulty, pain or severe distress.
Meanwhile, around 90% of customers overall have complied with the requirement across Scotland, according to the rail operator.
More than 20,000 free face coverings have been distributed to help people get used to the new normal of rail travel.
A limited supply of them are still available at more than 20 of the busiest stations across the country until the end of this week.
Staff on the rail network also have face coverings, as well as masks and visors for protection.
ScotRail Operations Director David Simpson said: "While it’s encouraging to see that most people across the country are following the requirement and covering their face when travelling, we need everyone to take personal responsibility for their travel choices.
"The mandatory wearing of face coverings helps keep you, your fellow customers, and our people safe.
"We’ll continue to do everything we can to help you get used to the changes in rail travel and that’s why we are providing face masks at our busiest stations for a limited time.
"Please only travel if your journey is absolutely necessary and be prepared with your own face covering over the coming weeks and months ahead."