Queen Elizabeth II on Thursday gave her royal assent to a bill that authorizes Prime Minister Theresa May to officially start Britain’s exit from the EU.

The European Union Notification of Withdrawal Act 2017 is now formally in effect after the Queen's approval, which is the final formality in legislation process for a bill.

The U.K. parliament’s upper house Monday night passed the bill without the proposed amendments, which had been overturned by the lower House of Commons earlier in the day.

The new act had to be legislated after the Supreme Court backed a court decision which ordered the government to receive a parliamentary approval before triggering Article 50 of the Lisbon Treaty.

The bill was passed by majority of votes at the House of Commons and later by the House of Lords, following the removal of suggested amendments by the lower chamber.

May has set the end of March 2017 as the deadline for triggering Article 50, a date after which negotiations between the U.K. and the EU will continue around two years to reach a Brexit agreement.

In June 2016, more than half of British voters voted in favor of ending the U.K.’s 46-year long membership with the bloc.

It resulted in the collapse of David Cameron’s conservative government after he resigned as prime minister.