DUP MP Jim Shannon, who racked up the largest expenses bill last year in Westminster, is being investigated by the Parliamentary spending watchdog.
The Strangford representative was paid almost £240,000 in taxpayer-funded expenses last year - more than any other MP.
The Independent Parliamentary Standards Authority (IPSA) has launched a probe into Mr Shannon’s mileage claims for 2017-18 and 2018-19, the Daily Telegraph reported.
In 2017-18, the MP claimed £51,000 in travel costs - around £4,250 a month.
The probe is headed by Tracey Hawkings, the IPSA's compliance officer.
Ms Hawkings, a former Detective Chief Superintendent at Essex Police, will look at whether the claims should have been paid.
IPSA raised concerns about travel bills and made a complaint to Ms Hawkings.
Mr Shannon's claims in the last year totalled £237,427 - around £90,000 higher than the average MP's expense claim.
The MP's expenses included office and accommodation costs as well as bills for two mobiles at £713 each - the cost of a high-end phone.
Mr Shannon's official Parliamentary credit card, which MPs use for expenses, has been suspended 13 times since 2015, data released under Freedom of Information Act has shown.
Cards are suspended when MPs break rules on expenses spending including failing to provide receipts within 30 days; spending that fails to comply with the rules and failing to repay money owed to the taxpayer for ineligible claims.
Any suspension comes after two formal warnings.
Mr Shannon, who sits on the Commons' Northern Ireland Affairs Committee, has previously had the highest expenses bills in Parliament.
In 2016 he had to repay nearly £14,000 in expenses following a previous IPSA investigation.
In 2014- 2015, Mr Shannon claimed nearly £60,000 for travel.
At the time IPSA said the incorrect claims were due to "a number of errors", rather than fraud.
A spokesman for Mr Shannon told the Daily Telegraph: "He will cooperate fully with the IPSA investigation and justify each and every claim. As an MP with a rural peninsula constituency and a very heavy workload he is confident that all mileage claims are valid.
"His 2017-18 mileage claim was £5,369.25 and for his staff mileage was £15,587.80."
