Amnesty International is calling on a council in Essex to stop a planned eviction of traveller families because it would leave them homeless.
After a prolonged legal battle Basildon Council has given 86 families living at Dale Farm notice to quit by 31 August.
Water and electricity supplies will be cut off following the eviction.
The council said forced clearance was a last resort and it was open to discuss future accommodation needs with the families.
Leader of the council Tony Ball said: "The council has spent the last 10 years attempting to find a peaceful solution to the illegal site at Dale Farm.
"A forced clearance has always been a reluctant last resort for us, but the travellers have left us with little option after exhausting the legal process.
"At heart a planning dispute about an illegal development on green belt land.
"It has absolutely nothing to do with the travellers' choice of lifestyle or ethnicity, and they are being treated in exactly the same way as any other citizen.
"We will keep talking to representatives at Dale Farm to try and resolve this issue without the need for a clearance and will continue to offer help with accommodation."
Jezerca Tigani, from Amnesty International, said: "Up to 400 people could be left homeless as a result of the forced eviction which would require them to vacate their plots without an authorised site to which they can take their caravans.
"The authorities must ensure that their actions do not break international law.
"They should instead talk to the residents of Dale Farm and reach a negotiated solution."
The eviction notice applies to plots on Dale Farm that Basildon Council says are "unauthorised developments".
The Irish Traveller families with 100 children between them own the land and claim they have been denied repeated requests to build residential properties there because of green belt restrictions.
Policing the clearance of the site is expected to cost up to £9.5m.