The DWP's recently published Guide to Volunteering states that lunches should not be included in expenses because income support and the jobseeker's allowance already "cover the cost of basic needs".
This has prompted 670 volunteer programme managers who belong to the Yahoo online discussion group UKVPMs to write to the department expressing their concerns about the guidance.
Kate Bowgett, manager of the volunteer development project for Off the Streets and into Work, said: "According to the new guidance, if I have a lawyer or someone from the City volunteering for me, I can reimburse their lunches, but if I have a person who is homeless and on jobseeker's allowance, I can't.
"Volunteers are already giving their time for free - they shouldn't have to give something else on top of that."
Volunteering England argued that the new guide was not only unjust, but also contradicted earlier government publications, including a recent NHS document that was given clearance by the DWP.
A statement on the charity's website says: "Volunteering England would be unable to support a position that runs counter to accepted practice in volunteer management, as well as to the Government's express aim of opening up volunteering to disadvantaged groups."
In April, the Home Office pledged £3m over two years to overcome barriers to volunteering encountered by disabled people, those without qualifications and ethnic minority communities.
Bowgett said: "All these groups are more likely to be on benefits, so this guidance is going to hit them the most."
V, which was established to recruit a million new youth volunteers, added that the new guidance could make young people think twice about volunteering.
Terry Ryall, chief executive of the organisation, said: "V believes that young people on benefits should not be out of pocket when they volunteer and that expenses directly incurred by volunteers in carrying out their activities should be reimbursed.
"There appears to be some confusion around Government advice regarding lunch expenses to people on benefits."