Tory MP Nadine Dorries is facing an investigation into her expenses claim by the parliamentary expenses watchdog.
The Independent Parliamentary Standards Authority (Ipsa) compliance officer Peter Davis said he had reason to believe Ms Dorries may have been paid travel and accommodation costs she was not entitled to.
"An investigation will be conducted into claims submitted under the following areas of the third and fourth editions of the MPs' scheme of business costs and expense - accommodation expenditure, travel and subsistence," he said in a statement.
A defiant Ms Dorries vowed to "go after" Ipsa, claiming the expenses body had simply targeted a high-profile MP to justify its funding.
She insisted she was "totally relaxed" about the allegations, saying they were completely unfounded.
One relates to a travel ticket claim that was submitted twice in error by a member of staff who had accidentally "pressed the button twice", she said.
"Ipsa was asleep on the bloody job not filtering out claims like that," she added.
Ms Dorries said Ipsa was also accusing her of subletting her flat because an electricity bill for a three-month period when her daughter was home from university was higher than her normal bills.
"I have never misclaimed one penny on my expenses," she said.
Ms Dorries remains suspended from the Tory whip following her appearance last year on ITV's I'm A Celebrity Get Me Out of Here!.
She added: "They need a high-profile MP to go after to justify their millions in funding. Well I'm going to go after them.
"All they want to do is get attention to show Ipsa is doing its job."