The charity Volunteering England has urged Theresa May, the Home Secretary, not to charge volunteers to use the proposed online criminal records checking system.
The proposed system, which would be created by the Protection of Freedoms Bill currently before parliament, is designed to alert employers to changes in potential employees' criminal records since their last check was carried out.
The new system has been designed to address the common complaint that volunteers and staff must have separate criminal record checks for every new organisation they work with.
In a letter to the Home Office last week, Volunteering England chief executive Justin Davis Smith said: "Although the government has confirmed that initial disclosures will continue to be free for volunteers, I would like an assurance from you that volunteers will not be expected to pay for this new checking and updating service.
"It is vital that volunteers are not left out of pocket by moves to simplify the system. This would run counter to the very welcome push to make the system less of a barrier for those wanting to give their time."
In a parliamentary debate in May, the junior Home Office minister Lynne Featherstone said: "At present, it is envisaged that if a volunteer wants to subscribe to the voluntary updating service, they will have to pay a subscription fee.
"That is still, however, under consideration, because we understand the position of voluntary organisations who say that a fee may be off-putting to volunteers."
If the bill is passed in its current form, each person who is the subject of a criminal records check would be issued with a unique number.
Charities and employers that wanted to recruit that person could enter the number on a website, which would then tell them whether any new information had been placed on the person’s record since the original check was carried out.
They would need to ask for a new criminal records check only if the website showed that new information was available. No details of the new information would be available on the website.