David Cameron faces a backbench rebellion tomorrow as Tory MPs seek to toughen up the Government's centrepiece immigration bill.
Around 70 Conservative backbenchers have signed a tweaked amendment to the legislation, originally tabled by Nigel Mills MP, which calls on the Government to reinstate restrictions on migrants from Romania and Bulgaria working in Britain until the end of 2018.
And a further 100 MPs have come out in support of a move by Tory MP Dominic Raab to completely block foreign criminals appealing deportation by claiming a right to a "family life" in the UK. The Bill returns to the Commons tomorrow.
The Prime Minister has reportedly been seeking to minimise a rebellion by reassuring backbenchers he shares their concerns, but has appealed for them to allow legislation to proceed uninhibited.
Mr Mills, Conservative MP for Amber Valley, attempted to have labour market restrictions for Romanians and Bulgarians extended before they were lifted on January 1.
The Government has refused repeated demands to publish or commission estimates of the numbers expected to enter Britain in the face of unofficial research predicting as many as 50,000 people arriving from the eastern European countries each year.
Mr Cameron rushed through new measures to ensure EU migrants are unable to claim out-of-work benefits for their first three months in the UK - but this was not enough to satisfy Mr Mills and has backers.
However, Mr Mills has lost the significant support of influential backbencher Douglas Carswell MP, who despite having signed the amendment announced on his blog he would no longer vote for it.
Mr Carswell wrote: "It is well meaning, but ultimately pointless displacement activity. A kind of Parliamentary grandstanding."
He added: "If we want to restrict the free movement of people into Britain from the European Union, then there is only one thing we can do - leave."
Meanwhile, Mr Raab's amendment would see the Home Secretary - rather than the courts - have the final say on whether an offender's family links are strong enough to allow them to avoid deportation.
Foreign criminals who can prove they face torture, ill-treatment or death in their home country will still be able to overturn deportation orders under separate human rights measures.
More than 200 foreign criminals successfully challenge deportation on human rights grounds every year with around 90% relying on the "right to private and family life" set out under Article 8 of the European Convention on Human Rights.
It is understood Tory whips are trying to persuade backbenchers to back amendments tabled by Stephen Phillips MP, which give the Home Secretary a duty to assess whether EU immigration is excessive and to assess the effects of new countries joining the EU.
Other proposals previously announced in the Government's Immigration Bill will see migrant access to the NHS restricted, while landlords, employers, bankers and DVLA staff will all be expected to take part in checks for illegal immigrants under the tough reforms.
An extension of the NHS charging regime was unveiled, which will see overseas visitors and migrants charged for accident and emergency treatment in England.
Migrants will also have to pay for primary care services such as minor surgery carried out by GPs, while prescription charges will be extended.
Other measures unveiled by the Home Secretary and Work and Pensions Secretary will see jobless migrants from within the European Union denied access to housing benefit from April this year.