Two offshore unions have called on the Health and Safety Executive to investigate Shell's operations in the North Sea.
Unions want reassurances over worker safety
Unite and the OILC believe the recent loss of key personnel from platforms Shell is selling means remaining staff may be unable to cope in an emergency.
The unions say they have had complaints from staff on five Shell installations.
Shell said the company had made sure the platforms had appropriately-trained safety workers.
The unions claim to have had concerns raised about the Cormorant Alpha, Dunlin Alpha, Tern, Eider and North Cormorant installations.
They said that since Shell announced the installations were for sale, communications between the company and the offshore workforce had deteriorated to the point it was impacting on operational safety.
Morale is also at an all-time low and the departure of several key personnel has created gaps in safety critical positions, according to the unions.
Jake Molloy, general secretary of the OILC union, said: "To ensure that the rig is operating safely then you need to have competent people, but these people are being eroded because of the forthcoming sale."
He accused Shell of failing to talk to the workforce, who had real concerns about their situation.
Mr Molloy added: "Staff are key to this operation. We want to impress upon Shell to act swiftly to retain these people with their wealth of knowledge and experience."
In June, Shell and Esso announced they were putting their joint interests in a number of North Sea oilfields up for sale.
Shell said "many" of its 400 onshore and offshore staff affected were expected to transfer to the new buyers.
A planned expansion of Shell's Aberdeen operational headquarters was also abandoned as a result of the decision.