Graham Benfield, the chief executive of the Wales Council for Voluntary Action, told the umbrella body's annual conference last week that the public funding of voluntary organisations raised inevitable questions about their independence.
"Is it possible to be working within the system one day but be publicly critical the next?" he asked delegates. Benfield said that there was an unspoken fear among charities that going public with criticism would lead to state funding being withdrawn.
"It is hard to identify any organisation that has actually lost funding as a result of criticising the government," he said. "It is more likely that organisations censor themselves for fear of implied or covert reprisal.
"Where organisations are in receipt of relatively large amounts of public funding, they are more likely to lobby in private than take their ideas to the media or opposition parties."
Julia Unwin, a former charity commissioner, will tell chief executives at Acevo's annual conference this week that self-censorship is a major threat to charities' independence. She claims in a booklet, entitled Speaking Truth to Power, that charities often exaggerate the consequences to public sector funding if they speak out.
"Third sector organisations frequently perceive a pressure to be silent, when, in fact, the evidence suggests otherwise," Unwin argues.
"Organisations that censor themselves, for whatever reason, are failing to articulate the experience of their members, service users or beneficiaries.
In the long run, the self-censorship that fears reprisals and seeks to pre-empt them is as dangerous for the freedom of the sector as the abuse of position by the powerful seeking to silence dissent."
At last week's Welsh conference, however, Benfield went on to argue that charities' independence could be eroded in other ways - through dependence on a single funder or the need to meet targets and comply with bureaucratic monitoring regimes.
"Prescriptive regulations can be such a diversion that organisations lose their independence and become, in essence, agents of the state," he said.
Stephen Bubb, the chief executive of Acevo, will tell his organisation's conference tomorrow that close links to government have brought voluntary organisations real benefits in shaping policy and improving service delivery.
"The gains for our clients have been striking. He will say: "Protests and marches were more appropriate 20 years ago than they are now that government is listening."