The Federation of Small Businesses (FSB) has called on communities secretary Sajid Javid to end a "shambolic" delay in allocating the business rate relief fund.
In a letter to Javid, the FSB urged the government to "get a grip" on the situation and make sure local councils start distributing the relief without further delay.
London authorities have been allocated £124m out of the £300m national relief fund announced in the Spring Budget to help businesses hardest hit by the property tax revaluation, but the fund has yet to benefit any firms.
"Small businesses in the capital are not benefiting from the discretionary pot," said Sue Terpilowski, London policy chair at the FSB.
"We are urging the secretary of state to write to all councils and for the mayor of London to put similar pressure on London councils to get this funding out of the door as many have seen punishing increases in their business rates bills this year."
Terpilowski said some small businesses are being forced to delay investment, avoid taking on staff or even closing their doors while they wait for government assistance with the "unacceptable" increases to business rates.
The FSB said it was aware of only 11 out of 33 London councils that have published details of their proposed local relief schemes: Bexley, Barnet, Brent, Bromley, Croydon, Greenwich, Haringey, Harrow, Hounslow, Merton, Richmond and Kensington and Chelsea.
However, it said it was not aware of any boroughs which have actually applied any reductions to ratepayer bills.
The implementation of the relief schemes has been delayed due to the need to update software, seek approval from MPs, consult with ratepayers and recalculate bills.
According to a survey taken by the FSB, three quarters (74 per cent) of London businesses that responded agreed business rates were the single biggest issue affecting their business prior to the election.
"All small businesses with the highest rises this year must get the help the chancellor and communities secretary intended when announcing this in the Spring Budget," the FSB said.