Caltrain fares could be going up for passengers who use cash to pay for their travel.

One-way cash fares, which can be purchased at ticket vending machines at Caltrain stations, could increase by 25 cents for each of the rail operator’s six zones, under a proposal being backed by the agency.

With the changes, a one-way trip between San Francisco in Zone 1 and Gilroy in Zone 6 will increase from $12.75 to $14.25. Under Caltrain’s proposal, round-trip cash day passes would increase by 50 cents, meaning two-way travel between San Francisco and San Jose would go up $25.50 to $28.50.

Caltrain spokeswoman Christine Dunn said that the increases are part of the agency’s ongoing transition to the Clipper card, the region’s one-stop transit fare. For Clipper card users, there will be no fare increases.

The agency will hold a series of public meetings to gather feedback on the plan, including a Jan. 24 gathering at the San Francisco Tennis Club at 6 p.m. On Feb. 2, Caltrain will hold an official public hearing at its board of directors meeting to discuss and possibly approve the proposal.

wreisman@sfexaminer.com