Facebook is blocking a number of Orange UK customers, both companies said on Friday.
Affected Orange customers trying to visit the social-networking website are receiving the notification "Access restricted: bad IP" and the message "You are trying to access Facebook from an IP (internet protocol) address that has been associated with abusive behaviour".
A Facebook spokeswoman said that some Orange customers had been affected, and that the company hoped to sort out the problem.
"We are aware that some people with Orange UK ISP addresses are having problems logging on to Facebook," Facebook told ZDNet UK in a statement. "We are working on a fix which we hope to roll out as soon as possible."
A number of customers have posted their dissatisfaction on Twitter about the situation. "Still not working. Why join another network when yours needs fixing? Orange, sort it out," wrote one user that goes by the name of 'rsc00'.
Orange was unable to say how many of its customers were being blocked at the time of writing.
Some users reported having no problems accessing the site. "My other half can't, but I can and haven't had a disruption all morning either. We're both on Orange," wrote a person with the username 'GalaxyPuppet' on Twitter.
Orange acknowledged the situation in a statement to ZDNet UK, but declined to give an explanation of the cause.
"We are aware that our mobile customers are currently having issues accessing Facebook via their handsets," said an Orange spokeswoman. "We are working with Facebook to fix this as a matter of priority and would like to apologise to our customers for the inconvenience this may cause them."
On 19 August, Orange confirmed that some of its users were having problems accessing its data network as reports of inability to access the service flooded Twitter.