TDM, which hosts web servers for about 250 customers, said it will terminate the accounts of firms that generate junk e-mail or use TDM resources to route it.
TDM's technical director Tarek Meliti said if more service providers took similar measures the spam problem could be greatly reduced.
Recent estimates from a US Federal Trade Committee put global spam volumes at between 40% and 75% of all e-mail traffic. Industry experts in the UK have estimated the cost to business to be billions of pounds a year in wasted bandwidth and storage resources.
Meliti said, "Our acceptable use policy says that those who send out spam or allow it to be sent across their servers or otherwise abuse the internet will have their contracts terminated. There are enough decent companies out there that we are happy to work with to mean that we do not need those that spam - it is better for us in the long run.
"It is easy enough for other companies to do this because lists of spammers are kept. If more of them did this it would force spammers to look abroad for hosting services and handicap them greatly."
Graham Titterington, senior analyst at Ovum, welcomed the move. "There have been mutterings about doing this for some time but this is the first time I have seen someone putting their head above the parapet.
"If the industry is to be regarded as mature, it is good to see someone doing something about it. It is a good idea but it raises freedom of information issues."
Have your say on spam, e-mail firstname.lastname@example.org