The construction contractor said in a statement that the Financial Conduct Authority is looking into statements released by Carillion between 7 December 2016 and 10 July 2017, during which time its shares tumbled 70%.
READ: Carillion says still in discussion with stakeholders regarding debt reduction options, expects to take action in the first quarter 2018
“Carillion is co-operating fully with the FCA,” it said.
Shares fell 3.9% to 17.2p in morning trading.
On July 10, the group issued its first profit warning for fiscal year 2017 and announced that Richard Howard would step down as chief executive.
The annoucement came four months after it reported a 5% decline in pre-tax profit to £146.7mln in the year to 31 December 2016, reflecting a weak performance in public private partnership projects and Middle East construction services.
Ahead of the 2016 results, on December 7, the company said it had seen a slowdown in orders due to changes in government spending plans since the Brexit vote.
Since July, its share price has plunged more than 90% after issuing two more profit warnings and saying it would breach its banking covenants as full year net debt balloons.
In its last trading update in December, it said it was still in discussions with stakeholders regarding its options to reduce debt and avoid a breach of debt covenants and expects to take action in the first quarter of 2018.
New chief executive Andrew Davies will begin on January 22, almost three months earlier than previously planned, to help lead the group's turnaround.