When Fatima Payman crossed the Senate floor to vote against her government she knew it would come with consequences.

The Australian Labor party has strict penalties for those who undermine its collective positions, and acts of defiance can lead to expulsion - a precedent with a 130-year history.

The last time one of its politicians tested the waters while in power was before Ms Payman was born.

But last Tuesday, the 29-year-old did just that - joining the Green party and independent senators to support a motion on Palestinian statehood.