Armed forces charity Help for Heroes has announced it will not accept donations from the far-right English Defence League.
EDL leader Tommy Robinson started fundraising after the murder of soldier Lee Rigby in Woolwich on Wednesday.
But a Help for Heroes spokesman said a fundraising web page set up by Mr Robinson would be closed, and no EDL donations would be accepted.
The charity said it does not accept donations from any political party.
The charity spokesman added: "He's the only one that's come to our attention but tonight we'll be doing a cross-count to make sure that anyone else that's saying they're EDL will not be allowed to fundraise for us.
"It's the same for any political party, we don't allow political fundraising. As a charity, we're non-political."
Mr Robinson's fundraising page showed he had raised more than £3,300 and he was aiming to raise £5,000 with a sponsored walk across London, but the page has now been closed.
On the page, he wrote: "I am going to walk from Westminster in west London to Woolwich in east London (just over 17 miles) to lay a wreath in support of our troops (Lee Rigby RIP).
"I plan to raise as much money as possible for Help for Heroes."
More than 1,000 EDL protesters gathered in London earlier and Mr Robinson addressed the crowd.
A smaller group of anti-fascist protesters gathered to oppose the EDL.
Scotland Yard said a total of 13 people have been arrested for public order offences. The figure is thought to include both EDL and anti-fascist protesters.