Mobile phone retailer Phones 4U has gone into administration, putting more than 5,500 jobs at risk.
The news comes as thousands of customers have placed orders for the iPhone 6 over the weekend. Apple's latest phone went on pre-order sale on Friday morning.
All 550 standalone Phones 4U stores will be closed today until a decision is made as to whether it can reopen for business, with the retailer blaming network EE for deciding not to renew its current contract with the business for the move.
Vodafone took a similar decision in September, leaving Phones4u without a single network partner.
Phones 4U chief executive David Kassler said: "A good company making profits of over £100 million, employing thousands of decent people has been forced into administration.
"The great service we have provided should have guaranteed a strong future, but unfortunately our network partners have decided otherwise.
"The ultimate result will be less competition, less choice and higher prices for mobile customers in UK."
Here's a Q&A to help worried customers:
What will happen to my contract?
The firm has said that all existing phone contracts bought through the company will be unaffected as they are serviced by the network operators – such as Vodafone or EE.
I've ordered a new iPhone 6 over the weekend. Will I still get it?
Any new phones – including the iPhone 6 – that have been ordered but not dispatched will be affected. These deals will not now be set up. However, Phones 4U has pledged to refund customers in full for any orders that will not be fulfilled.
I have Phones 4U mobile insurance. Will it be affected?
No, mobile insurance is provided and guaranteed through third parties. You should be able to find the name of the insurer on your policy documents.
How do I get in touch with the company?
The firm's website is no longer available. If you have any queries about your order or any other matters, call its customer service team on 0844 8712253 or the Freephone number 0800 0725858 (note: calls to this number will not be free from mobile phones).