Harbour Energy - the UK's biggest oil and gas producer - is reported to be selling its stakes in a number of major North Sea fields.
The move, which has been reported by Reuters this morning, comes as the Labour government prepares to bankroll renewable energy products by raising and extending the duration of taxes on oil and gas revenue.
The Budget, set to be formally announced on next Wednesday, is expected to include plans to rise in the Energy Profits Levy, commonly known as the windfall tax, as well as an extending it.
It is feared the move will trigger key players in the industry to pull out of the region and instead look to invest in assets overseas.
According to Reuters, Harbour Energy has launched a sale process of its stakes in the Armada, Everest, Lomond, Catcher and Tolmount fields as it seeks to reduce its exposure in the North Sea.
In a deal completed last month, the Harbour purchased Wintershall Dea's non-Russian portfolio for $11billion as it looks to diversify outside the North Sea, more than doubling its production in the process.
Harbour Energy did not comment on the sale process, insisting it was focused on the Wintershall Dea integration.
The government is also lining up new environmental guidance, for oil and gas projects, which executives predicted could further deter investments in the ageing basin, where output has dropped by around 75% since its peak in the late 1990s.