The European Union is taking legal action against the UK for allegedly failing to comply with the bloc's freedom of movement rules.
Brussels issued a formal notice to the British Government on Thursday giving them four months to "address the shortcomings".
In the opening of infringement proceedings, the European Commission claims that British law "limits the scope" of EU citizens living in the country.
Examples go back to 2014, including restrictions on EU citizen's ability to access Jobseekers' Allowance and "unjustified" lifetime bans on re-entry to the country are given by the Commission.
The alleged infractions mean that the UK is in breach of the 2004 free movement directive as well as EU treaty articles 21, 45, and 49.
Despite the UK formally leaving the bloc in December, the Commission highlights that until the end of the transition period, EU law including free movement continues to apply in Britain.
NEW The European commission has launched legal action against the British government for violations of EU law on free movement of people.— Jennifer Rankin (@JenniferMerode) May 14, 2020
Warns that UK risks citizens' rights agreed in Brexit withdrawal agreement. pic.twitter.com/C1Ibpj9aax
"We will look at what the EU has to say and we will respond in due course", a spokesman for Prime Minister Boris Johnson said.
This marks the first stage of infringement proceedings, which begin when a member start fails to enforce EU law and can lead to the European Court of Justice imposing financial sanctions.
The transition period for the UK to leave the bloc institutions such as the Single Market and the Customs Union ends in December 2020.
The formal noticed follows a European Commission debt report in July which claimed that Italy's large public debt in 2018 is a violation of EU budget rules and recommended launching infringement procedures.