Charities should be on the proposed register of lobbyists like other groups that have contact with politicians, according to the National Council for Voluntary Organisations and the Directory of Social Change.
But the NCVO has also warned that the register should not be operated in a way that would deter small voluntary groups from talking to MPs and ministers.
A Cabinet Office consultation, announced last week, asked whether charities and groups lobbying on their behalf should be required to join the planned register.
The consultation document, Introducing a Statutory Register of Lobbyists, asks, "should organisations such as trade unions, think tanks and charities be required to register?" and "should organisations that engage in lobbying on behalf of interest groups such as think tanks and charities be required to register?"
Sir Stuart Etherington, chief executive of the National Council for Voluntary Organisations, said in a statement: "We think charities should be subject to the same rules and regulations as those working for multi-client lobbying agencies.
"However, it is important to strike the right balance between promoting transparency and introducing any new bureaucratic burden. In particular, smaller organisations should not be dissuaded from engaging with the political system."
The statement said the NCVO would consult its members on how an "appropriate model" could be found.
John Lehal, managing director of the communications firm Insight Public Affairs, said: "Those large charities that have an ongoing relationship with government ministers should be on the register. But you have got to avoid a situation in which local charities do not feel able to contact their MPs, councillors or central government departments if they are campaigning on an issue."
Jay Kennedy, head of policy at the Directory of Social Change, said he would support any move towards greater transparency. "I don’t think charities should be in a different position from anyone else having meetings with government figures," he said. "And there is no reason why any charity should be afraid of being on the register.
"I can see that some people might view this as a move by MPs to curb charity campaigning, but I don’t see it in that way," he said.
A spokeswoman for Macmillan Cancer Support said the charity did not feel in a position to comment.