Ladbrokesâ€™ stock fell by 12%, while William Hill and Paddy Power dropped 7% and 3% respectively.
This week, the bookmaking community has been vociferous in its response.
A spokesperson for William Hill told The Spectator that his firm already paid more than its fair share of taxes: "The gambling industry contributes more than ÂŁ1bn to the Treasury, with a further ÂŁ400 million expected to be raised next year thanks to initiatives announced at the last Budget [increased duties on FOBT's]."
Ladbrokes director of external relations Donald McCabe echoed that sentiment, suggesting his company already paid more in tax than they earned in profit.
"We are not sure why an extra tax is being proposed on an industry already facing two tax increases and which pays out over 65 percent of all its earnings in taxes and levies."
Another Ladbrokes spokesman warned that the firm was already closing 40-50 shops this year, and more could soon follow.
"The pips are squeaking and we must surely now be given some stability to continue to support our employment and tax base while delivering for shareholders," he said.
William Hill chief executive Ralph Topping also questioned the political validity of the policy, telling the Sun: "Currently, costs are not passed on to the consumer, but that just would not be the case with this. The punter would take the hit â€“ and I cannot see how that would help Labourâ€™s popularity.â€ť
Industry feeling was succinctly summed up by one independent Yorkshire betting shop.
Labourâ€™s betting levy to be used for grassroots and problem gambling http://t.co/cDEfNqbnaW Think the well's almost run dry!— N Charles Bookmakers (@ncharlesbookies) July 24, 2014