A company with about 300 employees in Cumbria is being investigated by the Serious Fraud Office.
The Government body has announced it is investigating engineering consultancy Amec Foster Wheeler for suspected bribery, corruption and "related offences".
It has not released any further details.
The company has offices in Westlakes Science and Technology Park, Moor Row and at Sellafield as well as staff based at the BAE Systems submarine yard in Barrow.
A Serious Fraud Office spokesman said: "The director of the Serious Fraud Office has opened an investigation into the activities of Amec Foster Wheeler plc and any predecessor companies owning or controlling the Foster Wheeler business, together with the activities of any subsidiaries, company officers, employees, agents and any other person associated with any of these companies for suspected offences of bribery, corruption and related offences."
The company responded to this in a statement issued to the London Stock Exchange.
It said: "Amec Foster Wheeler takes its obligation to conduct business ethically very seriously and has in place a robust global anti-bribery programme, including a detailed code of conduct and anti-bribery and corruption policies. Amec Foster Wheeler continues fully to co-operate with and assist the SFO."
Amec Foster Wheeler announced a £2.2bn takeover with Aberdeen-based oil services company Wood Group - which trades as John Wood - earlier this year and has said the SFO investigation would be unlikely to have an impact on this.
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