Migrants who have crossed the Channel in small boats are to be housed in military barracks while their asylum claims are processed.
The Home Office has been accused of “exceptionally poor communication” over the plans.
Around 400 people including families are to be housed in temporary accommodation at Napier Barracks in Folkestone, Kent, from next week.
They are understood to include migrants who have crossed to the UK in small boats.
Local MP Damian Collins says he “cannot support” the decision and called on the Home Office to find “more suitable” accommodation.
A barracks in Pembrokeshire, Wales, is also being considered for use by the Home Office, the PA news agency understands.
The news comes after at least 168 people crossed to the UK on small boats on Monday.
At least 151 migrants crossed to the UK on Tuesday, with some landing on a beach in Kent.
In a joint letter to Home Secretary Priti Patel, Mr Collins along with the leader of Folkestone and Hythe District Council and the chairman of Sandgate Parish Council demanded that the decision be reversed.
They said: “We have great concerns about the impact this large open camp will have on the welfare of the local residential community and also those people in the asylum system who will be placed at the barracks itself.”
In a statement, Folkestone and Hythe District Council cited a “lack of consultation on this matter and the exceptionally poor communication with us”.
They added: “We are quite sure that members of the community will have many questions, and we are seeking clarification as a matter of urgency.”
A UK Government spokesman said: “During these unprecedented times, the Government is working with a range of partners and across departments to secure further accommodation and the MoD has offered use of some of its sites.
“When using contingency accommodation we work closely with organisations, including local authorities and law enforcement, throughout the process to ensure value for money and that vulnerable asylum seekers, who would otherwise be destitute, have suitable accommodation while their claims are processed.”
The two sites are part of the MoD training estate, PA understands.
Any training will be relocated to alternative sites or rescheduled, so there will no military personnel on site if and when they are used by the Home Office.
Also on Tuesday, immigration minister Chris Philp announced that 14 people who had crossed the Channel to Britain had been deported on Tuesday.
He said on Twitter that they had been removed to European countries following “last minute vexatious legal claims”.
Border Force have again been busy in the English Channel on Tuesday as more migrants have attempted to cross to the UK in small boats.
Several people believed to be migrants were seen after landing on a beach in Kent, while others have been brought into the port of Dover.
Among them were women and children too young to walk.
On Monday at least 168 people crossed to the UK aboard 12 small boats.
Among them were a group of 10 migrants pictured landing on Kingsdown beach in Kent and making off away from the shoreline.