Cabinet minister Ruth Kelly has apologised after breaking the rules on using taxpayers' cash for party political material.
MPs controversially awarded themselves a £10,000 "communications allowance" to help them "contribute towards public understanding of what this Parliament is for and what it does".
The Transport Secretary spent some of the money on a newsletter, but it fell foul of the regulations by using the word "Labour".
Ms Kelly told the Mail On Sunday newspaper: "There was no intention to do anything other than comply with the rules. However, I accept that greater care should have been taken over the exact wording, for which I unreservedly apologise.
"I will contact the Serjeant at Arms at the earliest opportunity and will, of course, abide by his decision in this matter."
Ms Kelly could be forced to repay the money.
Tory leader David Cameron has vowed to scrap the allowance - which critics said could be used as a "propaganda tool" by MPs in marginal constituencies.
