Western Australian Labor senator Fatima Payman defied party lines and to vote with the Greens on a motion to "recognise the State of Palestine".
By voting against her party, she 'crossed the floor' — a move that was and led to her being indefinitely suspended from the party caucus by Prime Minister Anthony Albanese.
Other consequences that can come with publicly opposing your party include missing out on pre-selection in future elections.
Despite the risks, crossing the floor has been a political tactic since the early days of parliament.
According to research by the Parliamentary Library, 296 individual parliamentarians crossed the floor between February 1950 and April 2019.
The Coalition participated in 96.8 per cent of floor crossing divisions compared to Labor's 3.1 per cent, and the Coalition accounted for 90.2 per cent of the individual MPs who crossed the floor compared to Labor’s 9.8 per cent.
So why are Labor MPs less likely to vote against their party?
Caucus solidarity
Since the 1890s, the Labor Party has pushed 'caucus solidarity': to present a united front to the parliament and voting public.
All decisions are debated in the caucus behind closed doors, then all members are expected to vote for it in parliament, regardless of their individual position on the issue.
Stewart Jackson, a senior lecturer in politics at the University of Sydney, said the more-than-a-century-old tradition started as a means of control.
It is very rare for Labor MPs to break 'caucus solidarity' and cross the floor. Source: Getty / Yoann Cambefort/AFP
"So, they said, 'Okay, from now on you're either in the party and you support what we want, or you're not in the party and you're out.'
"Can your colleagues trust you not to go off and do something else?"
Rob Manwaring, an associate professor from Flinders University's College of Business, Government and Law, said ideology also underpins Labor's tough stance on crossing the floor.
"The party puts a premium on discipline and also it puts a premium on collective solidarity," he said.
"That's built into the DNA of the Labor Party."
He said the Labor Party has historically viewed MPs as acting like delegates who support collectivism rather than representatives.
"In contrast, if you look at the Coalition in the early Liberal Party there was a much stronger focus on forms of representative democracy rather than delegatory ones," he said.
"It means that Liberal MPs were much more able to vote their conscience, focus on individual freedoms and consciousness rather than collective ones."
Crossing the floor has declined in popularity
During the 1960s and 1970s crossing the floor was far more common practice, particularly under the Menzies, Gorton and Fraser governments.
Liberal senator Reg Wright crossed the floor a record 150 times before his retirement in 1978.
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Fatima Payman crossed the floor: why is it so controversial?
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While crossing the floor has always been a rare occurrence, its popularity has declined in recent decades.
Jackson believes modern politics has become increasingly oppositional, leading to an 'us and them' mentality in the chamber.
"The polarisation of politics in the last 20 years I think has also gone a long way to ensuring that people don't cross the floor," he said.
"The [Coalition] are not going to support a motion put forward by Labor and vice versa but they'll happily vote together against a motion by the Greens, for instance."
Manwaring said modern election tactics could impede an MP's individualism.
"One of the things we see is an increasing professionalisation of political parties that focus on discipline," he said.
"As a result, it means that MPs probably have far less autonomy to speak their mind, particularly on areas of passion to vote against their own party than historically they would've done."
Career self-destruction?
Harold Holt, John Gorton, William McMahon and Malcolm Turnbull all crossed the floor at least once before becoming prime minister, a feat never achieved by a Labor politician.
So, what does the future hold for the Western Australian senator?
In a statement on Monday, Payman said she would abstain from voting on Senate matters "unless a matter of conscience arises".
"I will use this time to reflect on my future and the best way to represent the people of Western Australia," she said.
But the senator's future in the party is uncertain.
Manwaring said her Labor career is effectively over and Jackson said it looks bleak.
"I think Payman is probably finished as a Labor senator."
