Audits for the three years from 2015 by Grant Thornton will now come under the microscope.
Interserve entered a pre-pack administration last month.
In 2015 the company reported a pre-tax profit of £80m on turnover of £3.2bn.
In 2016 Interserve made a £94.1m loss from revenue of £3.24bn and in 2017 it made a £244m loss on turnover of £3.25bn.
The FRC said: “The Financial Reporting Council has commenced an investigation into the audit by Grant Thornton UK LLP of the financial statements of Interserve Plc for the years ended 31 December 2015, 2016 and 2017.
“The investigation will be conducted under the Audit Enforcement Procedure.”