Some charities are relying on volunteers "up to the point of exploitation", according to crossbench peer the Earl of Sandwich.
The former Christian Aid board member has raised concerns about how voluntary groups, as well as the commercial sector, are treating unpaid workers, and has called on the Government to protect them.
"Those who offer their services are often taken for a ride by people banking on their goodwill," he told the House of Lords during a debate on the voluntary sector last week. "Some charities and even small businesses depend on volunteers up to the point of exploitation."
The Government should strike a balance between protecting the concept of voluntarism and ensuring that contracted employees receive the minimum wage, the Earl added.
He said: "At present there is a potential conflict between the two when volunteers and employees share the same workplaces."