Liam Byrne says he wants to give a voice to neglected groups
The Cabinet Office has defended a £750,000 scheme to help small charities mount publicity campaigns.
Minister Liam Byrne fears small groups do not have the firepower of big charities when it comes to lobbying for changes in government policy.
He is setting up a fund to help those working with "vulnerable" people get their voices heard.
But senior Conservative MP John Redwood has attacked the scheme as a "crazy" waste of of taxpayers money.
Charities are banned from party political campaigning under Charity Commission rules.
They are allowed to lobby for changes in government policy and to raise public awareness of issues but a government review found some smaller groups were afraid to speak out for fear of losing their charitable status.
Under the scheme, a quango, Capacitybuilders, will seek out and fund up to 30 groups over the next two years. Further details will be announced in the spring.
Mr Byrne said: "Very often it's charities and campaigning groups who give a voice to people who don't get listened to enough.
"It's quite easy for politicians like me, or for think tanks or for big companies to put our arguments across, but for vulnerable groups it's often much harder.
"So what we want to do is find out how we can give those groups a megaphone too. So this announcement is about how we give the 30 best organisations a little bit of money to pioneer some innovative campaigning techniques on behalf of people who often don't have their voices heard in the public arena."
An aide said the scheme was not "not just about narrow lobbying" but could also be used to help community groups raise awareness of their work and experiment with new technology and ways of communicating their message.
He also stressed that it was not ministers who would decide where the money went and it could fund campaigns against government policy.
It would also be aimed at disadvantaged groups and those working with young people, which the aide claimed was a "timely" use of money in a recession.
But the plan was criticised by former cabinet minister, and leader of the Conservative Party's policy group on economic competitiveness, John Redwood, who said it was an example of government extravagance.
He said: "Why do they need to subsidise the political campaign industry?
"The government knows who these groups are. Why doesn't it just invite them in for a free meeting with a minister to talk about their concerns?
"Giving them money to advertise against government policy is just crazy."
At a time of recession, the government "should not be looking at more ways to spend money they have not got", he added.
"This is just a small example - and there are thousands of others - of this government wasting taxpayers' money."