Britain’s financial watchdog is investigating four large insurance brokers over information-sharing on aviation insurance, the companies said, in one of the first cases of its kind by the watchdog.

Aon, Jardine Lloyd Thompson (JLT), Marsh and Willis Towers Watson issued statements saying they were cooperating with the Financial Conduct Authority’s investigation, with Willis and Marsh adding the probe followed recent visits by the FCA to their offices.

“The FCA indicated that it had reasonable grounds for suspecting that Marsh Limited and others have been sharing competitively sensitive information within the aviation (re)insurance sector,” Marsh said in its statement on Friday.

Marsh said it was also conducting its own review of its aviation insurance business, with the help of an external law firm.

The FCA declined to comment. The watchdog was given new powers in 2015 to crack down on uncompetitive behavior, and had hitherto only mentioned one other enforcement case, in March last year, without elaborating further.

Aviation insurance – covering airlines against damages to their planes and injuries to passengers caused by accidents or war or terror attacks – totalled around 1.5 billion pounds ($1.9 billion) in gross written premium in 2015 across Lloyd’s of London and other London-based insurers.

The sector has been under pricing pressure for several years, due to increased competition given relatively high returns compared with many asset markets.

Aon said in a statement late on Thursday that it was “working diligently” with the regulator, but could not comment on the details of the ongoing investigation.

JLT, in a statement on Friday, said it was “providing all appropriate assistance to the FCA,” and Willis Towers Watson said in an emailed statement that it was “cooperating fully” with the FCA investigation.

The Insurance Insider reported late on Thursday that the FCA was investigating five aviation insurance brokers in London. The publication did not name the fifth broker. ($1 = 0.7822 pounds) (Additional reporting by Huw Jones.)