Hundreds of IT jobs are at risk today as Woolworths and MFI go into administration.
MFI made the announcement last night, while Woolworths appointed Deloitte as administrator this morning.
MFI has 190 stores across the UK and employs about 2,500 people, and Woolworths employs almost 30,000 people at over 815 UK stores, all of which will stay open for now.
Bosses at Woolworths have money available to pay staff tomorrow, but IT workers' future remains uncertain as talks continue to try and rescue the business, which has £385m worth of debt.
GMB, which represents some MFI workers, said they "couldn't say" how many IT workers would be affected.
The company has blamed falling demand and lack of credit for its financial problems.
The Union of Shop, Distributive and Allied Workers (Usdaw) represents workers at both companies and said its members are "devastated" at the news.
John Gorle, Usdaw National Officer, said, "We will be seeking urgent talks with the administrators to ensure that our members' future is at the top of their agenda and to understand the proposals for the businesses in the short to medium term.
"Obviously, the ongoing uncertainty surrounding the future of the stores will be of great concern to employees. Many of the staff have served the companies for many years and are extremely dedicated and loyal and we will be doing everything we can to help them through this difficult time."
In further evidence that the credit crunch has moved from the banking sector to retail, DSG International - the owner of Currys and PC World - reported a half-year loss of £29.8m. Retail group Kingfisher said sales at its B&Q chain were down almost 9%. The home improvement chain has been affected by the slow housing market and falling consumer spending.