Customers are protesting over the measures taken by web firm Fasthosts following a security breach.
Many have said the changes locked them out of their website
Following the attack on its customer database, Fasthosts asked customers to change their password for the webspace that Fasthosts looks after for them.
Last week Fasthosts unilaterally changed the passwords of customers who ignored this plea.
But the change has meant many small firms cannot access their website to administer their online shop or site.
The initial attack on Fasthosts took place in late October and the unilateral re-setting of passwords was carried out on 29 November.
A spokesman for Fasthosts said it took action after it became aware that a few customers who had not changed their passwords had "experienced a compromise" to their web space account.
Fasthosts will not say how many customers had their passwords reset only that a "number" were affected by its action.
The new passwords have been sent via the post to customers.
But many have complained that posting the password has effectively locked them out of their website until the delivery of the letter containing the new password.
In protest, some have set up websites to share information with other Fasthost customers.
The BBC has received many e-mail messages criticising Fasthosts for re-setting the passwords.
"This is causing severe problems for thousands of businesses and is only going to get worse," said Simon Metcalfe of SDM Insight.
Russell Wilkes of T6 consultancy said Fasthosts was doing a poor job of handling complaints and that phone calls and e-mail queries were going unanswered.
The Fasthosts spokesman said that the company had brought in extra staff to handle the volume of calls it was getting. It also said that customers could get their new passwords over the phone once the company had authenticated their identity.
The spokesman said further changes were due on 13 December when all passwords for e-mail services hosted by Fasthosts will be changed and apologised for the inconvenience this will cause.
"He added: "Unfortunately, the measures are necessary to fully ensure our customers' websites and data are fully secure."