The proposed reductions in staff, agency and contract resources are said to be driven by planned step downs in the work program at a number of sites.
Magnox is the management and operations contractor responsible for the NDA -owned 12 nuclear sites and one hydroelectric plant in the UK.
Since 2004, 11 of the 12 nuclear power stations have been decommissioned while the only operational nuclear facility at Wylfa in Anglesey, North Wales is scheduled to be decommissioned by the end of this year.
The job cuts also follow the merger of Magnox and Research Sites Restoration earlier this year.
The company would accommodate some employees in the wider Cavendish Nuclear/Fluor business, which owns Magnox.
However, workers union GMB energy national secretary Gary Smith said: "GMB will seek talks with Magnox and the Nuclear Decommissioning Authority (NDA) to discuss these job losses and the lack of progress on nuclear new build."
