Unlike South East Water and Southern Water, which have agreed an exemption, the company said it had no plans to extend dispensations for newly laid turf.
Other utility firms are still consulting on possible exemptions, which are due to come into force in early April. The Thames Water consultation ended last week.
HTA policy manager Gary Scroby said: "We’ve not seen an official notice but this is disappointing for our members and colleagues in the Turfgrass Gowers’ Association.
"Without that particular exemption it will be an even tougher season. There are serious commercial ramifications for some small and medium sized businesses."
Current Thames Water exemptions cover people with severe mobility problems holding Blue Badges, those using drip irrigation and car-washing and window-cleaning businesses.
Meanwhile, in better news for the industry, all water companies implementing bans form 5 April will exempt drip watering systems.
This means that Sutton & East Surrey, Veolia Central and Veolia South East have come into line with Thames, South East, Anglian and Southern Water companies.
BALI is encouraging members to add their voice to the lobby by sending their template letter to their local water company /member of parliament.
Download the BALI pro-forma letter here.