There will be major push back against any attempts to alter the Triple Lock, the Sinn Féin leader has predicted.
The Triple Lock is the requirement for Government, Dáil and UN approval before more than 12 members of the Defence Forces can be deployed on overseas missions.
The Government has stated that the mechanism is no longer fit for purpose, and it will soon publish plans to change it.
Mary Lou McDonald was speaking at a meeting of the Irish Neutrality League in Dublin.
"We will fight like hell to stop them...our message is very clear, hands-off Ireland's neutrality," she said.
Ms McDonald said the country’s neutrality goes to the very essence of what it means to be Irish, and it is hardwired into the nation and any proposed changes should be put to the people in a referendum.
The Triple Lock is Ireland’s guarantee to its people and to the world that its defence forces would never be part of an illegal war, Senator Frances Black told the meeting.
She said the Government intended to change the Triple Lock quickly and they must be resisted and held accountable.
The senator warned that any changes would erode this country’s standing internationally at a time when its independent voice on issues like Gaza was never more important.
Independent TD Catherine Connolly said the meeting has one message and that is that neutrality matters and people will not give away the Triple Lock.
People Before Profit-Solidarity TD Paul Murphy said the Government will try to use its majority to ram through changes to the Triple Lock and mass protests will be needed to halt this plan.
Tánaiste Simon Harris has described the Irish Neutrality League's stance as "disappointing".
"We cannot allow others have a veto over where we send Irish peacekeepers," he said.
"What would the opposition propose we do if the UN didn't renew mandate for our peacekeepers in Lebanon?" Mr Harris asked.
He said it was shortsighted by Opposition politicians to not even wait until legislation is published.
