The statement is regarded by some political analysts as a thinly veiled threat to withdraw support during the next General Election in the UK.
The influential Muslim Association of Britain issued the warning after George Galloway was expelled from the party after he was accused of calling on British troops to disobey orders to fight in Iraq.
The association said on Friday that the decision has been met with anger and disappointment by Britain's Muslim community.
"The Labour Party ... has wasted an opportunity to mend its failing relations with the Muslim community," it said in a statement.
"George Galloway was always and will continue to be seen as a champion of issues close to the hearts and minds of Muslims, and he will always enjoy their full support and backing.
"At a time when political apathy is widespread and feelings of despondency are rife, one would have thought that George Galloway’s sincerity, principled stands and promotion of truth... were exactly what our democracy needed."
The comments come as Galloway prepares to meet constituency members in Glasgow on Saturday to decide whether to resign his parliamentary seat and spark a by-election.
"George Galloway was always and will continue to be seen as a champion of issues close to the hearts and minds of Muslims, and he will always enjoy their full support and backing"
Muslim Association of Britain
If he does decide to stand as an independent candidate, it is widely expected he will sweep to victory and heap further embarrassment on embattled Prime Minister Tony Blair.
"The expulsion of Galloway could prove disastrous for Labour if a sudden by-election is called.
"Galloway has huge support in Glasgow which also has a large Muslim community. This could prove very damaging and if he turns the antiwar movement into a political force, Blair will rue the day they kicked him out," said a Labour party activist on Friday.
Galloway is respected by Britian's two million Muslims for his impassioned defence of Palestinian rights, and his principled opposition to Western foreign policy in the Muslim world.
His views have struck a chord with a community which is frustrated by the British government's backing of Israel and the US-led invasion of Iraq.
After being expelled for his remarks on an Arabic TV station, a characteristically defiant Galloway rejected the Labour Party charges.
He told Aljazeera net: "Just as Mr Blair's disasterous war was based on a lie, so they have expelled me based on a lie.
"I didn't call on Arabs to attack the Britsh army, I called on British soldiers to disobey illegal orders which is an obligation on all armies since the Nuremburg trials.
"All I did was oppose a liar from dragging my country into a war."