A minister has been asked to pay back £500 parliamentary expenses he claimed for a constituency letter featuring Labour's rose emblem.
Sadiq Khan was ordered to pay back the money
The Committee on Standards and Privileges said Assistant Whip Sadiq Khan breached rules by not keeping it "proportionate and discreet".
The newsletter was sent out in Mr Khan's Tooting constituency in April.
Mr Khan said Labour gained no advantage because there were no elections, but the complaint was upheld.
In a letter to the Parliamentary Commissioner for Standards Sir Philip Mawer, who upheld the complaint against him, Mr Khan said his office had sought approval for the newsletter from Commons authorities.
"My office and I would not have submitted the invoices to be paid out of Parliamentary allowances had we not been assured by the Department of Finance and Administration that they would be deemed payable - which I took to mean that it must have complied with the existing guidelines," Mr Khan wrote.
In its report published on Thursday, the committee did accept the party's advantage was "limited".
But it said: "The use of such a prominent logo was a clear breach of the rules and Mr Khan should therefore repay £500 of the sum he has claimed from the communications allowance in respect of this publication."