The concerns have prompted the suggestion that grant-making trusts might be most effective if they directed their grants towards activities, often by smaller charities, where statutory funding was not available.
David Emerson, chief executive of the association, told Third Sector that trusts were always wary of the effects of statutory funding and that some of them might re-examine the "appropriate direction" of their future grants.
He was expanding on remarks he made at the association's fringe meeting at the Labour Party conference last week, when he said he feared the sector could lose its "fire in the belly" as a result of delivering more public services.
"More voluntary organisations are tending to do what they are paid to do, rather than what they are deeply passionate about," Emerson told the meeting.
This could prompt charities to move towards contract compliance rather than focus on the outcomes of their work.
Emerson questioned whether grant-making trusts might become more effective by focusing their grants on areas where statutory funding did not exist, often served by smaller charities.
A future role for trusts could be in funding advocacy, he argued.
"We have to ensure that the enabling and empowering quality of the voluntary sector is not undermined by the delivery of public services," Emerson concluded.
But service delivery charities were given a boost at another fringe meeting, where Home Office minister Hazel Blears promised to make it her mission to drive forward the voluntary sector's public services agenda.
Blears told the meeting, organised by the National Council for Voluntary Organisations, that it was now "decision time" in the debate. "(Charities minister) Paul Goggins and I are about to embark on a mission to talk to our colleagues in other government departments and see if we can identify some big areas where public services could be delivered in a very different way," she said.
But she added that charities needed to ensure they would not resemble the public sector. She emphasised: "I do not want the voluntary sector to be like the public sector is now. The very reason for doing this is to do something different."
However, Blears said more responsibility should also be handed to end-users.
"For me, the only reason this agenda is worth considering is that you engage ordinary people in a chance to shape their own futures and their own destinies," she said.