London (CNN)British Prime Minister Theresa May has again come under fire, with the European Parliament warning it may veto her proposals on EU nations living in the UK because they risk creating a "second class of citizenship."
EU Parliament threatens to veto UK's 'damp squib' offer to EU nationals
May has been criticized on a regular basis since making public her plans to extend rights to the 3.2 million EU nationals living in Britain after Brexit.
The proposals put forward by May were described as a "damp squib" in a letter written by EU Parliament chief Brexit negotiator Guy Verhofstadt and leaders of the parliament's four main parties, and published Monday.
"The proposal falls short of its own ambitions to 'put citizens first'. If implemented, it would cast a dark cloud of vagueness and uncertainty over the lives of millions of Europeans," the letter read.
According to the British government's plans, a new "settled status" would allow EU nationals who have lived in the UK for five years to remain and enjoy access to health care, education and other benefits.
EU nationals who have spent a shorter time in the UK would be allowed to remain until they reach the five-year point, at which stage they can apply for settled status. Others who arrive after an as-yet-undisclosed cut-off date will benefit from a "grace period," expected to last two years.
May has promised families will not be split up, but her government says that all EU citizens and their families must obtain an immigration status irrespective of when they arrived in the country.
The proposal is dependent on British nationals living in EU states being offered a reciprocal deal.
But Verhofstadt and his fellow European politicians says the proposal falls short of the promises made by the Vote Leave campaign, which said it would treat EU citizens "no less favorably than at present" once Britain withdraws from the EU.
"The British government proposes that -- the day after Brexit -- Europeans obtain the status of 'third country nationals'," the letter read.
"These nationals would get fewer rights in the UK than British citizens are offered throughout the EU. Europeans will not only lose their right to vote in local elections, their future family members will also be subject to minimum income requirements, and it is unclear what the status of 'post-Brexit' babies will be.
"The British proposal carries a real risk of creating a second class of citizenship."
The European Parliament will have a vote on the final Brexit deal, which will include the rights of EU nationals and British citizens living in EU states.
While it does not engage in direct talks with London, it will press Michel Barnier, the EU's chief Brexit negotiator, to secure a better deal before Britain leaves the bloc in March 2019.
The letter also insists that the European Court of Justice plays a full role in enforcing the rights of both British and EU nationals -- a demand which the UK government will see as infringing upon a red line. May has said the rights of EU citizens should be enforced by UK courts.
"We will never endorse the retroactive removal of acquired rights," the letter added.
"The European Parliament will reserve its right to reject any agreement that treats EU citizens, regardless of their nationality, less favorably than they are at present. For us, this is a question of basic fundamental rights and values, which are at the heart of the European project."
In response, Damian Green, Britain's first secretary of state, insisted the "basic rights" of EU citizens will be protected by the government's proposals.
Speaking to the BBC, Green said, "... somebody who is here now will keep the rights that they already have and we hope and expect that British citizens living in other EU countries will keep the rights that they already have there."
He added: "If we're outside the European Union, then we clearly have to have basic immigration rules to check that somebody coming is from the country they say they are coming from and is a citizen of that country, all that kind of thing.
"But that's not an insuperable barrier. We all fill in forms when we go on holiday and have to get visas and things like that in other parts of the world. But the basic rights will be preserved, so that should not be an obstacle to a final deal."