A US activist investor has upped its stake in Rolls-Royce (LON:RR.), putting pressure on the jet engine maker to change course.
ValueAct has more than doubled its stake in Rolls to 10%, thereby firming up its position as the turbine group's biggest single investor.
Rolls shocked markets last week by warning on profits and giving a gloomy view of its prospects for 2016.
The group said its lucrative jet engine after-sales business was facing pressure as airlines opted to buy new rather than keep older models going.
It also highlighted a downturn in its marine power business as oil and gas companies, who face falling crude prices, cut back on investment in rig support vessels.
And a broker pointed to the costs of developing a new engine for the Airbus A380 "super-jumbo".
The shares have fallen from 1035p in April to 540p on Thursday, having suffered a fall of about 20% when Rolls issued its trading statement last Thursday.
ValueAct has a reputation for keeping large stakes for several years and pushing for big changes.
Rolls has always argued that its diverse product range, ranging from jet engines for civil airlines and military aircraft to nuclear power plants and ship propulsors, protects it from a downturn in any one business sector.
But some investors have urged the company to sell its marine business and ValueAct could press it to make disposals of less profitable activities.
The US hedge fund has formally requested a seat on the board to reflect its stake, according to a report in the Financial Times.
The FT reported a spokesman for Rolls as saying that its board had not yet decided whether to back ValueAct's request.
New chief executive Warren East, who has carried out a review of the company, is due to brief investors next week on his plans.