The Pituitary Foundation has adopted new objects that lawyers say are not legally charitable and have not been authorised by the Charity Commission.
Jon Danzig, a former volunteer for the charity, submitted a number of complaints about the medical charity to the commission last week.
Many of them relate to disparaging emails that the foundation sent to its members urging them not to speak to him.
Now Danzig has discovered that the charity submitted new objects to Companies House last April. Examples include "to continue to be known as a supportive and caring organisation" and "to maintain a highly professional administrative and organisational structure".
The charity's previous objects, which are still listed on the commission's website, include the treatment of and the promotion of research into pituitary disorders.
Jonathan Burchfield, a partner at law firm Stone King Sewell, said none of the new objects were charitable in law. "They are a list of aims and strategic objectives rather than legal objects," he said. The changes would not take effect unless they were authorised by the commission, he said.
A spokeswoman for the commission confirmed that it had not given the foundation permission to change its objects. She said the matter would be considered as part of the assessment of Danzig's complaint.
Terry Lloyd, chair of the foundation, said he was unaware of the complaint but would provide the commission with any information or assistance it needed.
Danzig said his motive in making the complaints was "to save this charity, not to destroy it".