A new legal challenge to Brexit has been launched in a bid to stop or slow the U.K.'s plans to leave the European Union.

The case argues that the U.K. cannot formally extract itself from the EU because this would violate the terms of a treaty it signed in 1998 to secure peace in Northern Ireland.

The complicated treaty — called the Good Friday Agreement — laid out rules about political leadership in the region to end decades of violence.

McIvor Farrell Solicitors have filed the case in the high court in Belfast. An initial hearing is scheduled for next week.

The law firm also argues that an exit from the EU would be unlawful until members of parliament vote to approve the move.

The British public voted by a slim majority to leave the European Union in June, but most voters in Northern Ireland wanted to remain. The referendum was not legally binding, but only advisory in nature.

Here's a rundown of the other legal challenges to Brexit:

Maitland Chambers

Law firm Maitland Chambers was the first to present a lawsuit in court. Further hearings in this case are set for October.

Maitland Chambers' senior barrister Dominic Chambers says that, contrary to popular belief, the new U.K. prime minister -- Theresa May -- does not have the legal authority to trigger the nation's formal exit from the EU.

That can only happen once members of parliament approve the move, he argues.

The Maitland Chambers case will be heard together with another related challenge by law firm Mishcon de Reya.

A decision is expected by the end of October. Any appeal would go directly to the Supreme Court.

1,000+ barristers

More than 1,000 lawyers across the U.K. recently signed a letter to remind the prime minister and members of parliament that while the results of the referendum must be acknowledged, they are not legally binding.

They are calling on members of parliament to vote on leaving the EU before making a final decision.

However, no formal legal action is expected to follow this letter.

And while many lawmakers do not believe Brexit is in the nation's best interest, it's hard to see them ignoring the referendum result.

The expat challenge

British citizen and World War II veteran Harry Shindler, 95, argues that hundreds of thousands of British citizens living abroad were denied the right to vote in the referendum, which should nullify the referendum results.

Anyone living outside the U.K. for over 15 years was denied a referendum vote.

Shindler, who has been living in Italy since the early 1980s, said the fact that he was denied a vote was arbitrary and undemocratic.

Shindler has exhausted his legal options in U.K. courts, but his challenge is now being heard by the United Nations Commission on Human Rights, he said.

The U.K. government has already rejected a petition calling for a second referendum, signed by more than 4 million people.

Targeting Leave campaigners

Barrister Anthony Eskander at the firm Church Court Chambers in London, said he is considering assisting clients with a criminal case against the individuals who led the campaign to leave the EU, asserting that they misled voters with broken promises.

He expects these individuals, including former London mayor Boris Johnson, could be found guilty of misconduct in public office, which would be a criminal offense.

However, the case could take months or years to wind through the courts and would not necessarily stop the government from triggering an exit from the EU.

Regardless, he told CNNMoney the case would still be worth pursuing because campaigners should be held accountable for their "propaganda".

--CNN's Peter Taggart contributed to this report