An increasing number of councils are trying to ban or restrict the number of people who face-to-face fundraise on their streets, known as "chuggers".
Some charities have recently been criticised for employing agency reps who allegedly deploy aggressive tactics.
But organisations have hit back, saying they provide much needed funds in difficult times.
Sky News tested one area where there had been a large number of complaints.
Our undercover reporter was approached by reps working for Amnesty International outside Angel station in Islington, north London.
He told the fundraiser six times that he did not have much money and would like to "think about it" before committing to a donation.
The rep repeatedly criticised his decision to take time considering, saying: "What is there to think about?
"I mean imagine you were in a situation like that.
"You went to another country and you said, 'I think there should be democracy here' and they lived under a dictatorship and you got put in prison for saying that and nobody knew where you were.
"How soon would you want somebody to help you?"
For eight minutes he persisted. "Are you going to go 'I'd like to help you but I want to think about it?'," he went on.
"Imagine if I get everybody on this street today to give 20p a day to this charity. We'd be able to save so many people, but you know not everybody is that generous."
Islington Council has been considering banning face-to-face fundraisers.
Christine Lovett, director of the Angel Business Improvement District, told Sky News there had been numerous complaints from the public and that it had affected business on the high street.
She said residents liked giving to charity but "the nature of the complaints are the harassment and the intimidation that some people feel happens from some of the street fundraisers.
"My concern is that some of those charities, if they knew how they were being sold would also have concerns around their behaviour."
Amnesty International declined an offer to look at our recording but in a statement said: "While face-to-face fundraising is only one of several different methods of recruiting new supporters it provides a terrific way of meeting members of the public and explaining our work, as well as providing income for vital human rights work.
"Of course, it is essential that fundraisers behave appropriately and at Amnesty International we have a dedicated training manager and closely follow the Public Fundraising Regulatory Association's code of conduct."
Other charities agree that this method of fundraising is crucial to achieving their goals.
Action Aid's fundraising director, Peter Reynolds, said: "They are important to us financially.
"We need to find 20,000 new supporters this year in order to maintain and increase the work we do with the world's poorest people, and they provide an important contribution in finding those supporters for us."
Fundraisers should abide by an Institute of Fundraising code, which prohibits sellers from blocking people or following them down the street, but we spoke to one former "chugger" who explained that not all reps stuck to the code.
Nigel Wilson said: "More successful chuggers would follow people down the street, sometimes walk alongside them for maybe 10, 20 paces.
"One tactic was to tell people 'you've dropped something', stop them, get their attention and then you're in."
Recently, Aldeburgh & District Macmillan Cancer Support Committee in Suffolk closed down in protest at the use of pushy agency fundraisers.
The move was agreed unanimously by the 15 committee members after they received complaints of "high pressure" tactics during door-to-door sales pitches.
The Public Fundraising Regulatory Association estimates that £130m of charities' annual revenue comes from street and door gifts, £45m of which is raised on the street.
The association has helped 42 councils across the country draw up agreements with charities to restrict street selling, reducing numbers on the street and limiting the locations and the number of days they can operate.