Members of a secretive fund-raising body associated with Federal Treasurer Joe Hockey are being invited to pay $3000 each to be part of an exclusive budget day event attended by his most senior staff and key ministers.

The fund-raising body, the North Sydney Forum, offers exclusive access to Mr Hockey, often in private boardrooms, in return for political donations in the form of annual membership fees of up to $22,000.

But the forum and Mr Hockey refuse to disclose the names of its members. Mr Hockey has declined to say what meetings and discussions he has had with them because his diary is ''confidential''.