Top British judges are hearing claims that the government of Prime Minister Theresa May cannot start formal negotiations for the UK to leave the EU without parliamentary approval.
The battle over Brexit reached the Royal Courts of Justice in London on Thursday amid intensifying political disagreement over the controversial issue.
The High Court will hear two and a half days of argument that could decide whether ministers can invoke Article 50 of the Lisbon Treaty, without Parliament passing a new law.
The legal dispute is over who has authority to invoke Article 50, which says that any member state may leave the EU “in accordance with its own constitutional requirements.”
The legal challenge was launched after the June 23 referendum, which saw 52 percent of British citizens voting to leave the EU.
Gina Miller, an investment manager and anti-Brexit campaigner, is leading the legal challenge over the government’s right to invoke Article 50.
She said ministers were attempting to "bypass Parliament" by not seeking a vote, but opponents said it was a "naked attempt to steal the referendum by the back door.”
If the court decided that Parliament has authority to trigger Article 50, the majority of MPs might not be in favor of leaving the EU.
On Monday, UK Brexit Secretary David Davis said the government would reject any attempt to undo or delay the result of the June 23 referendum.
His remarks came after a number of MPs from all sides called for a parliamentary vote on ties with the EU in the future, warning that Brexit would pose a “great danger.”
Davis, however, said that the government should "respect” the British people’s decision, noting that “no one should seek to thwart the will of the people.”