Internet providers in Britain are getting tougher with those websites that use spam to drum up business.
Code aims to stop the amount of spam on networks
A new code of practice adopted by net firms lets them close e-commerce sites using junk mail marketing, even if the spam comes from elsewhere.
It is not clear if the policy will cut the flood of spam messages because most of it comes from outside the UK.
Net firms hope to reduce junk mail by getting the code adopted by the nations used by spammers to send messages.
The tough policy means that online shops and e-commerce websites will be shut down if the visitors they get have arrived because of a junk mail message.
It aims to tackle those firms that send spam from one network but maintain their actual trading site on a reputable net operator.
By tackling the web shops that profit from spam, UK net firms hope to remove the financial incentive to send junk mail.
It also wants to tackle those websites that offer spamming tools, such as CDs full of e-mail addresses, for sale.
The code of practice was drawn up by the London Internet Exchange (Linx), where most of the UK's net firms swap traffic between each other's networks.
The revised code signed by 150 net firms at an extraordinary general meeting of Linx.
Link acknowledged that there could be problems enforcing the code if one spammer tried to get a rival shut down by sending junk mail on their behalf.
As most UK net firms already shut down firms that "spamvertise" for customers, it is unclear how much difference the changes will make to the amount of junk mail in circulation.
A study out this week showed that the majority of spam, 86%, originated in the US.
The UK's Linx hopes to get the improved code adopted by Ripe - the international body that draws up policies for net firms in more than 90 nations.
It will also push organisations such as the OECD to adopt the code of practice.
Linx's former policy, drawn up in May 1999, has been widely adopted in the web world as a model of best practice.