Sir Stephen Bubb, head of Britain's charity chiefs, has come under fire amid accusations he printed Parliamentary invitations to his House of Lords 60th birthday paid through his own charity's donations.
Sir Stephen is chair of Acevo, which is funded by membership fees from over 1,500 charity chiefs, and earns £100,000.
He has courted controversy for defending charity bosses' large pay packages, dismissing criticism of them as a "disgraceful distraction".
On Friday, Acevo was forced to admit that the organisation paid for half of Sir Stephen's 60th birthday, a tea party for 90 out on the House of Lords Terrace estimated to cost £1,500.
However, former Acevo officials have indicated that the ultimate bill could be far higher as over 100 glossy parliamentary invitations were printed for guests.
The source told the Huffington Post UK: "Over one hundred invites were ordered for the House of Lords party. Sir Stephen had his assistant write out every invite by hand. Personally I'm unsure what cost would have been incurred but I'd have thought he could have done generic invites rather than pay the surplus for fancy invites.
"As I'm aware only senior staff for invited from Acevo, leaving the majority of the work force unable to attend his birthday party that was funded by our company"
House of Lords invites would cost at least £285 to produce 30, so a 100 invite print run would cost nearly £1,000.
Tory MP Priti Patel told the Huffington Post UK “These revelations give an alarming insight into the way money at an organisation funded by charities and taxpayers is being spent.
"Sir Stephen Bubb has been very outspoken about defending excessively high salaries but so far silent on these serious claims.”
Charlie Elphicke, a Tory MP who is member of Public Administration Select Committee, said: "Spending charitable funds in this way seems highly inappropriate. These funds are donated to help people in need, not birthday bashes for the great and good."
The Huffington Post UK tried to get in contact repeatedly with Acevo, but no-one was available.
Alongside his second income, Sir Stephen receives a salary as chair of the Social Investment Business Group of £11,857, whose board meets just five times a year.
He has campaigned for charity board trustees to be able to be awarded higher pay-packages, telling MPs last year: “Why should we be able to say to these charities that they can't pay their trustees if they want to?”.