Australia's Liberal-National Coalition, the country's main opposition, has split after a row over hate speech reforms, casting the future of Liberal leader Sussan Ley into doubt.

The centre-right Coalition, which has been on rocky ground since a resounding election defeat last year, had been divided over how to respond to reforms moved by the government after a terror attack targeting a Jewish festival at Bondi Beach killed 15 people.

The Nationals ultimately refused to follow the shadow cabinet decision on the laws.

"Our party room has made it clear that we cannot be part of a shadow ministry under Sussan Ley," leader David Littleproud told reporters in Brisbane on Thursday.

Announcing the split on a national day of mourning for those killed in the shooting on 14 December, Littleproud said the Coalition "was made untenable".