Three of the region's hospitals are understaffed, according to the Care Quality Commission.
The health watchdog has issued Southampton General Hospital, St Anne's House in East Sussex and Princess Royal Hospital in West Sussex with warnings after carrying out inspections .
Labour - which released the information - said the findings reflected a "toxic" combination of cuts and reorganisation.
The government said the number of NHS clinical staff had risen since 2010.
Health Secretary Jeremy Hunt said he expected "swift action" to be taken by those named.