Conservative MPs are being investigated by the Parliamentary Commissioner for Standards over the alleged misuse of House of Commons dining rooms.
Commons dining rooms cannot be used for 'direct' financial gain
Sir Philip Mawer launched a preliminary inquiry after two Labour MPs said 22 Tories were using the facilities to raise party funds.
The rooms cannot be used for "direct financial or material gain" by parties, sponsors, or any person or group.
A Tory spokesman said the party did not believe it had broken any rules.
Labour MPs Kevan Jones and John Mann met Sir Philip last week and handed him a dossier claiming 22 Tory MPs had broken the rules.
The allegations are thought to concern patrons' clubs which charge a membership fee in return for access to dinners in the Commons.
Conservative chairman Frances Maude told BBC Radio 4's World at One he was glad Sir Philip Mawer was looking at the use of Commons dining rooms.
He said he was confident the party had operated within the rules but it was a "grey area".
He went on: "If it were not possible for there to be any political dinners in the House of Commons then obviously that would be slightly absurd and the dining rooms would be empty half the time.
"There is some ambiguity in the rules and Sir Philip Mawer will clear it up for us and we will follow whatever he says."
A Tory spokesman added: "This appears to be an issue which affects all the political parties.
"We have asked Sir Philip to clarify the rules. If he has received an official complaint from Labour MPs then it is his job to investigate properly.
"We believe we've broken no rules and look forward to his conclusions."
A spokeswoman for Sir Philip confirmed a complaint had been made but gave no further comment.
But Labour MP Kevin Jones told the BBC: "They're using private dining rooms for direct fundraising, not only for sitting members of parliament but also for target Liberal Democrat and Labour seats.
"And they're also using the offer of a House of Commons dinner as an inducement to join various numbers of organisations - mainly called patrons' clubs".