Cabinet ministers Ed Balls and Yvette Cooper are being investigated over allegations they are improperly claiming expenses for their second home.
The pair, who are married, face criticism for claiming more than the £20,000 MPs are supposed to collect on their second home in London.
Mr Balls, children, schools and families secretary, and Ms Cooper, chief secretary to the Treasury, are now under investigation by parliament's standards watchdog.
Parliamentary standards commissioner John Lyon's office is leading the probe.
Both Mr Balls and Ms Cooper deny wrongdoing. Together they could claim £40,000 on their second home but have chosen to take far less than this.
Some dispute which is their second home - they share a house in Yorkshire, near their constituents, which they say is their main home.