Nobel peace laureate Mairead Maguire is in custody, facing deportation from Israel after being arrested at an airport in Tel Aviv on Tuesday.
Israeli authorities said they refused Ms Maguire entry because she took part in an attempt to break the blockade of Gaza.
Her lawyers said she would challenge the ruling at a full court hearing in Tel Aviv on Friday.
Ms Maguire won the peace prize in 1976 for her work with the Peace People.
In June of this year, she was on board the Rachel Corrie, one of a number of ships in an aid flotilla which was refused entry to Gaza and boarded by Israeli forces.
An earlier attempt to break the blockade led to the deaths of nine Turkish citizens after an Israeli military raid on their ship.
In 1976, Ms Maguire founded Women for Peace, which later became the Community for Peace People, along with fellow Belfast woman Betty Williams.
The organisation was formed after the tragic deaths of three children.
On 10 August, Ms Maguire's sister Anne, was walking along a road in west Belfast when an out-of-control car plunged into them.
The car's driver, IRA man Danny Lennon, had been fatally wounded by a British army patrol which was chasing him.
The car plunged into the Maguires, instantly killing six-week-old baby, Andrew, who was in his pram and his eight-year-old sister, Joanne, who was on her bicycle.
Their brother John, just two-and-a-half, died the following day in hospital.
Their mother, Anne, was maimed physically and mentally - and would take her own life some years later.
It was Mairead who made a grief stricken plea for peace on television.
It struck a chord with communities across Northern Ireland and the Peace People was formed.
They marched in cities and towns such as Belfast, Enniskillen and Ballymena and held one of their most high profile rallies in Trafalgar Square in London.
Thirty-four years on, Ms Maguire continues to work for peace at home and abroad.