Pro-EU membership supporters argue with a leave campaigner outside the High Court, on the second day of the lawsuit of Gina Miller, a founder of investment management group SCM Private in London, Monday, Oct. 17, 2016. Rival protesters have gathered outside the High Court in London, where lawyers are battling over whether the government has the power to trigger Britain's exit from the European Union without approval from Parliament. (AP Photo/Frank Augstein)

LONDON - People making threats against a woman challenging the British government over its European Union exit plans will face "the full vigour of the law," a High Court judge said Monday.

Financial entrepreneur Gina Miller is the lead claimant in a lawsuit arguing that the government can't trigger Britain's exit from the EU without approval from Parliament.

Prime Minister Theresa May has said she will invoke Article 50 of the EU treaty — triggering two years of official exit talks — by March 31. She is under pressure from lawmakers to give them a vote first, but insists that is not necessary.

Miller says that she has received abusive and threatening messages because of the case. Three judges will consider their ruling after two days of hearings end Monday.

Judge John Thomas told the court that "it is simply wholly wrong for people to be abusive of those who seek to come to the queen's courts."

He said "the full vigour of the law" would be used against those responsible if the abuse continued.

Miller's lawsuit hinges on whether May can begin divorce proceedings with the EU without a vote in Parliament. A majority of Britons voted in June to leave the EU, and lawyers for the government argue that the prime minister is entitled "to give effect to the will of the people."

Lawyers for Miller and the other claimants say the executive branch of government should not be allowed to remove citizens' rights without lawmakers' approval. When Britain leaves the EU, its citizens will lose the automatic right to live and work in other EU member states.

Since June's EU membership referendum, relations between the victorious "leave" side and disappointed "remain" voters have become tense and sometimes abusive.

On Monday a Conservative councillor in Guildford, southern England, was suspended by his local party for setting up a petition advocating that support for Britain rejoining the EU should be made an act of treason. Treason felony carries a maximum life sentence.

Paul Spooner, Conservative leader of Guildford Borough Council, said councillor Christian Holliday's proposal was "completely mad."

News from © The Associated Press, 2016