Peter Davis of the Independent Parliamentary Standards Authority (Ipsa) said he had reason to believe that the mid-Bedfordshire MP may have been paid travel and accommodation costs to which she was not entitled.
"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.
Dorries has denied the charge of wrongfully claiming expenses, saying that the watchdog is "targeting" her because of her "high profile" status.
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