The Boston Carmen’s Union president said Monday that a dozen MBTA fare-collecting machines last week were left too full of money to work after T management changed the routes of the employees who drive across the region to collect cash fares.

James O’Brien said that 12 of 84 machines last Monday were affected — and riders got free trips because of it.

“We received notices from employees that fare gates were being left open to accommodate the amount of riders who had to be given free trips due to inoperable fare machines,” he said at a meeting of the T’s Fiscal and Management Control Board.