Volunteer instructors with the Bristol Sea Cadets could be facing clean air zone costs of around £1,000.
Bristol Sea Cadets chair Tim Moran says volunteer numbers are rapidly declining and many of its current instructors are retired and drive non-compliant cars.
People are charged £9 per day for entering Bristol's clean air zone (CAZ).
If an instructor were to attend two weekly meetings, it means they clock up £18 in fees a week - which is £936 a year.
Now the charity, which teaches marine and boating skills to children and teens, has put out an urgent call for more volunteers.
Mr Moran said: “If you include weekend events, our instructors face paying about £1,000 per year for driving non-compliant vehicles. That’s a very significant chunk of their pensions, it’s an outrage.”
The sea cadet syllabus, which offers a number of courses to different age groups, requires up to 10 instructors at each meeting.
Mr Moran said: “We need an instructor for each course and historically we’ve always just got there, so this is a big shout-out for more volunteers.”
He added that the park-and-ride facilities close too early for use by volunteers, parents and their children as their meetings finish at 9.30pm. He also said the number of children attending meetings has dropped, particularly those coming from the south of Bristol.
Mr Moran said CAZ costs, the cost of living crisis, and rising energy prices mean the charity's costs have tripled.
He said: “For the past 10 years, we’ve operated on a budget of £20,000 to £25,000, but this year we’ve got to find £60,000. It’s a crying shame.”
A spokesperson for the council said the government's guidance and requirements for the clean air zone had been followed.