Unions fear that if the joint venture with the French company Societe Nationale Poudres et Explosifs (SNPE) goes ahead then Royal Ordnance's Bridgwater plant in Somerset may close with the loss of hundreds of jobs.
Mr Portillo will be greeted by workers from the factory bearing placards attacking the Government's failure to intervene when he arrives to deliver a speech at the Royal United Services Institute in London. The placards will read "Ou est Portillo?" and "Nous sommes les Miserables".
Royal Ordnance is now part of British Aerospace, which has been pursuing a series of joint ventures with European partners in defence and aerospace.
The Bridgwater plant is the country's only manufacturer of TNT-based explosives and certain other explosives used in artillery shells. The plant also makes explosives for large airdrop weapons such as the 1,000lb bomb, and polymer bonded explosives which are safer to handle and store.
Jack Dromey, national secretary of the Transport and General Workers Union and spokesman for BAe's five industrial unions, said: "We support European collaboration to prevent American domination of our continent's defence manufacturing base. But no previous joint venture has surrendered vital strategic capacity. The French government is actively involved and is determined to defence French national interests. Michael Portillo is silent."
A spokesman for Royal Ordnance said: "There is overcapacity in the industry and that is one of the reasons we are looking at doing this joint venture. But no decisions have yet been taken."
The Bridgwater plant is one of three that make up Royal Ordnance's explosives and propellants division. The other two are at Bishopton in Scotland and in Holland.Reuse content