Plans for an asylum seeker welfare centre in Calais will encourage illegal immigration to the UK, the Tories say.
About 500 foreign nationals currently sleep rough in Calais
Shadow immigration minister Damian Green said the government was being "appallingly complacent".
The plans have been dubbed Sangatte Two after the French town's refugee camp, which was shut in 2002 over concerns it was a base for people trafficking.
The Home Office said the centre would not be the same type of complex and border controls had been boosted.
The Liberal Democrats said the Tories' reaction to the plans was "cynical and hysterical".
Home affairs spokesman Nick Clegg said: "Once again the old Tory party re-emerges to score cheap political points on the emotive issue of immigration.
"What do the Conservatives propose to do with the thousands of people who have congregated in Calais - simply consign them to mass destitution?
"We should be tightening our border controls with a national border police, but this is not incompatible with recognising the need for the most basic of welfare provision for migrants and refugees."
The Sangatte refugee camp in northern France closed in December 2002 following an agreement between the UK and French governments.
Unlike Sangatte, the new centre which has the support of the mayor of Calais and local charities, would not provide accommodation.
It would offer food, showers and information and advice for about 500 foreign nationals who currently sleep rough in the area.
The mayor of Calais said a final decision on the centre would be made at the end of April and it could be open by November.
But Mr Green said providing facilities in Calais "just encourage people to arrive there to try to come to this country illegally".
He told the BBC: "It's disappointing that our own Home Office doesn't seem to be doing anything about this.
"We all know that the only reason why all those people are there is to try to break the law and try to come to Britain illegally, and dangerously in many cases."
Richard Ashworth, the Conservative MEP for the south east, said the new centre had the "right intentions, but ultimately they are creating another hub for people wanting to enter the UK unlawfully".
In February, he wrote to French interior minister Nicolas Sarkozy, asking him to intervene.
"Organised people traffickers would focus their efforts on the centre, and the congregation of people intent on entering the UK would recreate the images we saw before Sangatte was closed," he said.
Fall in numbers
A Home Office spokesperson said: "There have always been humanitarian services for migrants in the Calais area.
"However, our understanding from the French government is that there are no plans to establish a new Sangatte-style centre in the Calais area."
Brodie Clark, head of UK Border Control added: "The numbers coming into the UK have dropped substantially largely due to the dramatic effect of establishment of UK immigration controls in Calais.
"In achieving these results there has been substantial co-operation from the authorities in France."
Official figures show the number of illegal immigrants detected entering Kent from Calais fell 88% from more than 10,000 in 2002 to 1,500 in 2006.