UK mobile phone retailer Phones 4u said it is seeking the appointment of administrators from PricewaterhouseCoopers after its key partner EE notified the company that it would not be renewing its network agreement.
The contract, which ends in September next year with the UK's biggest mobile operator EE - which comprises T-Mobile and Orange, was crucial to the business for Phones 4u after it lost a similar contract with Vodafone earlier this month.
The company, majority-owned by private equity firm BC Partners, said the unexpected decisions by both Vodafone and EE "have come as a complete shock to the business."
The decision has led Phones 4u to shut all of its 550 stores that employ about 5,600 workers, until a decision by the administrators is made on whether the business can be reopened for trading, the company said.
"Today is a very sad day for our customers and our staff. If the mobile network operators decline to supply us, we do not have a business," Chief Executive David Kassler said in a statement.
The process of the appointment of an administrator is under way and is expected to occur on Monday, the company said.