AAP
About 100,000 mostly young Australians have won back their right to vote following a landmark High Court decision that could have significant impact on the 2010 election.
In a majority decision, the High Court has declared parts of the Electoral Act unconstitutional and invalid, meaning thousands of Australians will now be able to have their say on August 21.
Political analysts say it has the power to alter the final numbers come polling day, particularly in the Senate.
Advertisement: Story continues belowAustralian Electoral Commission (AEC) staff are now scrambling to contact those missing 100,000, with election day now just over a fortnight away.
The High Court ruling overturned amendments introduced by the Howard government in 2006, which tightened the electoral requirements for both new and existing voters.
Instead of having seven days to enrol after the election writs are issued, new voters - mostly those had just turned 18 - had only until 8pm on that day.
Those wanting to amend their details on the electoral roll were forced to get in contact with the commission within three days, rather than the usual week.
Lobby group GetUp, the Human Rights Legal Resource Centre and Mallesons mounted a joint legal challenge, arguing the changes were unfair and unconstitutional.
GetUp director Simon Sheikh said the changes in 2006 were "political manoeuvres" by the coalition, and Australian Greens leader Bob Brown agreed the laws were politically motivated.
"This was John Howard trying to cut young Australians out of voting because the coalition's not doing so well there," Senator Brown said.
He said the Labor government under Kevin Rudd had attempted to return to the old seven-day cutoff, but was thwarted by the coalition and Family First's Steve Fielding in the Senate.
"This is why it's so important for the Greens to hold the balance of power," Senator Brown said, saying support from young people for his party was on par with that for the coalition.
Mr Sheikh believes the 100,000 or so potential votes could help sway the final election outcome.
"(It's) an extraordinarily large number," he said.
"With marginal seats across the country and an extremely tight election, (this) could have a massive impact."
The opposition's accountability spokesman Michael Ronaldson defended the 2006 changes as moves to strengthen the integrity of the electoral roll.
It was now open to rort and abuse, he said.
But Special Minister of State Joe Ludwig welcomed the High Court's decision, saying it restored democratic rights.
The ruling also affects the electoral protocols for many Australians living overseas and their families.
Mr Sheikh said he hopes the court's ruling opens the door to more progressive changes to the electoral system.
About 1.4 million Australians - or six per cent of the population - are currently not enrolled to vote, with 70 per cent in the 18-39 bracket, according to the AEC.
"Today's case is the next step in getting them on the electoral roll," Mr Sheikh said.
The High Court ordered the commonwealth pay the plaintiff's costs, although Mr Sheikh declined to say what Mallesons had forked out for the work.
About 20 lawyers worked around the clock on a pro-bono basis