Traditionally, they have used exhibition stands at party conferences as one of their key lobbying tools. But with rising fees and competition from high-budget corporate stands, many find themselves priced out of the market.
A stand at the Liberal Democrat conference this year costs a charity about £1,000, while a premium slot at the Labour conference can be up to £8,000. Consequently, the RNID is scaling down its operations, and NSPCC is only setting up a stall at the Labour conference.
"We are just not convinced that the through traffic at the other conferences is significant enough to warrant the expenditure of having a stand," said Sereena Hirst, parliamentary advisor at NSPCC.
"Purely on a stand basis, smaller charities can struggle to compete with the flashier efforts of corporations and those of the larger charities."
Last year, however, RNID's stand did rival its lavish corporate sector counterparts. It was designed like the Tardis from Dr Who, with a soundproof booth used to offer hearing tests.
"We were campaigning for the modernisation of audiology departments and chose a time travel theme because departments had been stuck in a time warp," said Mark Morris, RNID's head of parliamentary and legal affairs. "It worked very well, and people even queued for the test".
But without a generous budget matching the scale of a charity's grand designs, it can be difficult to make a stall stand out.
One innovative approach came at last year's Labour conference, when Greenpeace ran a free shuttle bus to ferry weary delegates from hotels to the conference and fringe meetings.
This gave the campaigning group 10 minutes to talk to their passengers about the importance of public transport.
"It really was a good initiative - everyone came away thinking the world of Greenpeace," said Morris.
Such stunts are rapidly becoming a must if charities want to be noticed, because delegates are bombarded with information.
"You are wasting your time if you just hand out leaflets," said Morris. "You have to be clever with your approach."
Many smaller charities opt for a muted presence, and simply send a representative to the conference for a day or two. And the low-key approach can pay dividends.
"From MPs to voluntary sector people to activists, the conferences are full of useful contacts, so they are a great opportunity to network," said NCVO parliamentary and campaigns officer Pete Moorey.