Vaz set up Silver Star six years ago after being diagnosed with diabetes himself and the charity now operates worldwide to raise awareness of the debilitating and life threatening condition.
But bank statements belonging to one of the male prostitutes, purportedly shows two payments of £150 each being received from a man linked to Silver Star.
The first of these payments was made on August 5 three weeks before the alleged liaison although the prostitutes claimed they met Vaz - a married father of two - on more than one occasion.
There is no suggestion that anyone associated with Silver Star was aware what the payments were for, but a former trustee of the charity said the matter had to be investigated as a matter of urgency.
Retired Dr Malde Modhwadia, who stepped down from his volunteer role three months ago, said: "We need to find out what has been going on. There will be an investigation. Our charity is a worldwide charity, with its headquarters in Leicester and we do good work raising health awareness for diabetes sufferers. Mr Vaz founded it and is the patron.
"I cannot believe he would use anyone linked to the charity to pay cash into an account to pay for his escorts. It would be too clear and obvious. We are a completely open charity and I'm in the process of making inquiries."
Referring to revelations about Vaz he said: "He is my constituency MP and I am really shocked. He has a wife and kids and has been leading a double life, not that being gay is a crime or illegal but he is a family man."
Fellow MPs also said there were urgent questions to be answered about the alleged payments from the charity's account.
Tory MP, Andrew Bridgen said: "I will be writing to the charity commission to ask if they will investigate the financial links and relationship between the charity, Mr Vaz and paying for male prostitutes."
Vaz's Labour colleague, John Mann, also said the Charity Commission needed to establish exactly what had happened with the payments.
He said: "I am sure they are going to do that straightaway. They have not got any choice. The best thing is for Keith to outline everything and then people can make their own judgement. If it was true it would be horrific."
Officials at the Charity Commission also said the regulator would be looking at the payments to ensure there was nothing untoward.
A spokesman said: "We will assess this information to determine whether there is any role for us...we will be looking in to it."
The charity's executive director, Hanif Pathan, could not be contacted for comment last night.
The lurid allegations threaten to finally derail the 29-year career of a politician, who has been dogged by controversy.
In 2001 he stood down from his role as Europe minister over claims that he had tried to help smooth the British passport application of the billionaire Hinduja brothers and he has also twice been investigated by the parliamentary standards watchdog over his financial dealings.
In 2012 it emerged that Scotland Yard had also probed his finances amid claims he had large unexplained payments going into his accounts.
One MP also claims he reported Vaz to Leicestershire Police and the Commons Speaker last year over allegations surrounding his private life.
But Vaz was said to be determined to prove his innocence.
A friend claimed the two prostitutes had actually been painters who had come to redecorate a new flat he had bought close to his family home in Stanmore, Middlesex.
The friend said that Vaz did not drink and questioned whether he could have been drugged.
But a source at Trinity Mirror, the publisher of the Sunday Mirror, said the newspaper stood by its story: "This is not a sting. This is not a set up, we have not entrapped him into anything he was not doing anyway."
Labour leader Jeremy Corbyn appeared to play down the row, saying that it was "hasn't committed any crime that know of. As far as I'm aware it is a private matter, and I will obviously be talking to Keith".
Other Labour MPs were less supportive, including Jess Phillips, MP for Birmingham Yardley, who said: "I don't give a toss what people do in their private lives, I do give a toss about sexual exploitation. Nothing funny about today's news."
