The AA has fired its executive chairman, Bob Mackenzie, for “gross misconduct”, with immediate effect.
Its statement gave no further details as to the reasons for his departure, but an AA spokeswoman said it was “a personal conduct matter”.
Shares in the AA sank by up to 18% as the roadside recovery firm also said trading had been affected by “erratic workload patterns.”
Mr Mackenzie had been the AA’s executive chairman since June 2014.
The company said he would be replaced by non-executive chairman John Leach, while Simon Breakwell – who was a founder of Expedia – has been named as acting chief executive.
Mr Mackenzie had led the AA since overseeing a management buy-in of the company in June 2014, which led to its shares being listed on the stock market.
Before that, the company had been owned by private equity firms Permira, Charterhouse and CVC.