High street retailer BHS is expected to enter administration today, putting 11,000 jobs across the UK at risk.
The chain is in debt to the tune of £1.3bn, including a £571m pension fund deficit.
David Gill, of the shopworkers' union, NASDAW, said he was "very concerned" about the situation.
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He added: "We are seeking urgent clarification from the company and urging them to change their attitude to trade unions and begin a dialogue with us at this difficult and worrying time for staff.
"We also urge the company to comply with the law, consult staff and USDAW as the union for BHS workers on the future of the business.
"I am writing to members working in BHS to reassure them that we will provide the support, advice and representation they require," he added.
The clothing and furnishing chain has been struggling to modernise since it was bought in 2000 by Sir Philip Green, who sold out last year for £1. New owners Retail Acquisitions - "a group of little-known financiers", says Mark Kleinman of Sky News – aimed to raise £160m in funds to turn around BHS's fortunes, but have failed to do so.
"A few weeks back it looked like they had secured a urgent lifeline by getting approval from landlords and other creditors to reduce its rent bill at its more than 160 stores," Kleinman said. "But a separate £60m loan that the company required has failed to materialise."
The BBC says Retail Acquisitions planned to raise an additional £100m through property transactions. The group sold their Oxford Street lease in London for £30m, far less than expected.
It had been hoped that Sports Direct owner Mike Ashley, who bought the lease on BHS's Sunderland store for £2m, might take over at least part of the chain. He is said to have been reluctant to take on the pensions debt, however.
Retail analyst Phil Dorrell told the BBC the likelihood is that BHS will now be sold off "store by store", meaning the brand will disappear from high streets, although the shops won't all "close today".
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