When Australia was newly federated the Labor Party shared the most policy with the Deakinist Liberal Party. They formed alliances in the early days even. However, the first Labor Parliamentarians acted like the wheeling dealing politicians of old and were quickly wedged or maneuvered out of parliament by the other parties and politicians.

As a result the Labor Party developed the pledge whereby Labor politicians would vote the same way as the Labor party executive determined. This changed Australian politics entirely as Labor was now a voting bloc. Judith Brett writes:

The insurmountable barrier between the Deakinite Liberals and the Labor Party was not Labor's policies not its attitude toward the state, but the nature of the party's organization: the demands which it made on its members to subordinate their own views and judgements to the collective will of the party and the implications this had for parliamentary government.

The problems Labor's organisation posed for the Liberals was particularly apparent in Labor's hostility to alliances. Labor simply refused to play the parliamentary game as it had hitherto been played, and parliamentary leaders found themselves stalled at every turn as they tried to put together workable majorities in the usual way.

This voting as a bloc in the way the party executive requires is known as the pledge and has led to Australian politics being dominated by absolute party discipline. The conscience vote - which Labor does not allow - is the rarity and exception. The horse trading that the American Congress would do where party dissent was tolerated is unheard of in Australia. It is becoming rare in the United States too though. James Fallows commented that in an overhead conversation in Congress:

"GOP member: 'I'd like this in the bill.'

"Dem member response: 'If we put it in, will you vote for the bill?'

"GOP member: 'You know I can't vote for the bill.'

"Dem member: 'Then why should we put it in the bill?'

While the Republican Party only has enough votes for a filibuster in the Senate in order to stop bills coming up for debate, that is a more a convention than a constitutional or legislated rule. But it does seem to show that the Republican Party is able to maintain party discipline - I am not sure where from though; there is no Executive in power and I don't see the US party structures outside of Congress as that strong. The recent purity test was ignored for instance. So I am not sure where it is coming from.

More A speech by Petro Georgiou describes the history of the pledge.

More Cyclical link to John Barrdear who argues that it is fund raising enabling this.
Via Slashdot Nick Minchin starts an op-ed in the SMH with, "Underlying the Rudd Government's plan to screen the internet is an offensive message: that parents cannot be trusted to mind their children online." How frustrating for Australians that they are stuck with this bad policy and a change in government has not tanked it. This legislation started in 1999 with the Liberal Party - of which Nick Minchin was a cabinet minister in - and now the Labor Party, for reasons of similar politics, have continued the bad policy.
Tim Dunlop has the best coverage of the Labor policy including a comparison with the Liberal announcement. Doing the same analysis with the Labor tax brackets as with the Liberal ones leads to this graph.

Again it is from the 2003-2004 Tax Statistics which is the most up to date publicly available data. (more)
Cam Riley: South Sea Republic. Freedom, liberty, equity and an Australian Republic.