Brain injury group Headway has urged charities not to stage sponsored cycle rides unless they make helmets compulsory.
Around 150 cyclists are killed on Britain's roads each year. Lucy Fairbrass, a fundraiser at Headway Surrey, says some voluntary organisations continue to put profit at the expense of safety by arranging events at which helmets are optional.
"Charities wouldn't dream of letting someone abseil down a building without a rope or safety helmet, so why do they allow people to take part in bike rides without the proper protection?" she said.
Headway has been lobbying the Government to introduce legislation to make helmets mandatory for cyclists or to run a campaign highlighting the dangers.
Rather than wait for changes to the law, Fairbrass believes charities should take the lead by refusing to allow volunteers to take part in events without protective headgear.