Rock band Rage Against The Machine is ahead of X Factor winner Joe McElderry in the race for the Christmas number one, early sales figures suggest.
A Facebook group aiming to get the band's 1992 hit Killing In The Name to the top of the festive chart has attracted more than 750,000 members.
But McElderry's debut The Climb, out on CD on Wednesday, is expected to catch up by the weekend.
The Official Charts Company (OCC) said it is "a very exciting battle".
It is understood that there is a 10% margin in sales between the two singles after Sunday and Monday.
McElderry's song was only released digitally after his victory in the X Factor final at midnight on Sunday, giving it less time to rack up sales for this week's chart than Rage Against The Machine.
X Factor judge Simon Cowell has criticised the internet campaign, calling it "stupid".
Prior to the final of the ITV talent show, he said: "I think the campaign's aimed directly at me."
The Facebook page includes a link to homeless charity site Shelter, which has raised nearly £30,000 in donations.
Rage Against The Machine, meanwhile, are signed to Epic Records, which is part of Sony BMG, the same label as McElderry.
Ladbrokes has re-opened its betting for the number one Christmas single just 24 hours after closing it.
Ladbrokes spokesman, Nick Weinberg, said: "Earlier this week it looked a done deal. Now Joe appears to be facing an almighty battle for top spot.
"This Christmas could be the first time in a long while that we see a genuine competition."
McElderry is at 1/3 with Rage Against the Machine at 2/1.
The OCC's Martin Talbot said "two different records have captured the nation's imagination".
"According to our initial sales estimates, there is no doubt that this tussle is far from over," he added.