Dorries expenses probe.
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.
Nadine Dorries denies any wrongdoing