Green Party Euro-MP Caroline Lucas will be among speakers at a meeting examining alternatives to waste incineration.
The meeting on March 7 comes a few days before Brighton and Hove City Council and East Sussex County Council are due to sign a £1 billion waste disposal contract.
The deal includes building an incinerator to burn rubbish at North Quay, Newhaven.
Other speakers at St John Sub Castro Church, Abinger Place, Lewes, include Gary Smith of the GMB union, and city councillor Rik Child.
Ms Lucas said: "We need to recognise what people throw away as an opportunity for secondary use and for employment. The throw-away society is not sustainable and governments at every level, local, national and international, must take the lead on addressing these issues."
Unions are concerned the private finance initiative will put pressure on the operator to keep costs low and hit workers' terms and conditions.
The meeting starts at 7.30pm.
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