Sir Philip Green has been sent a warning notice from the Pensions Regulator which could see the former BHS owner being ordered to pay towards the company's pensions deficit.
The watchdog said it has begun enforcement action "to seek redress on behalf of the BHS pension schemes".
It has sent warning notices to the retail tycoon and his holding company Taveta, as well as serial bankrupt Dominic Chappell and his firm Retail Acquisitions Limited, to whom Sir Philip sold the business for £1.
The notices "set out evidence" to support the use of the regulator's powers to demand a "specified sum of money" to "put ongoing support in place for a pensions scheme", to be agreed with the watchdog.
BHS went into administration with a £571 million pension scheme deficit shortly after being sold for £1 by Sir Philip to Mr Chappell.
The regulator said that following a "complex investigation" it issued the notices, each of which runs to more than 300 pages and sets out the arguments and evidence as to why the watchdog thinks Sir Philip and Mr Chappell should be liable to support the BHS pension schemes.
Pensions Regulator chief executive Lesley Titcomb said: "We have been clear in our public commitment to make significant progress by the end of 2016 and the issue of these notices meets that commitment.
"Our decision to launch enforcement action is an important milestone in our work to attain redress for the thousands of members of BHS schemes who have been placed in this position through no fault of their own.
"Issuing warning notices at this time reflects the outcome of our investigations and that we are yet to receive a sufficiently credible and comprehensive offer in respect of the BHS schemes.
"We continue to pursue the best deal for members of the BHS pension schemes. If parties wish to approach us with settlement offers, that course remains open to them."
Sir Philip and Mr Chappell will now have a specified period of time to respond to the notices.
The regulator's case teams will then consider these before passing the case to its determinations panel.
The panel, which operates at arm's length to the case teams, will then decide whether to exercise the regulator's powers to compel payment.
Commons Work and Pensions Committee chair Frank Field said: "We are not surprised that the Pensions Regulator has, like all the rest of us, lost patience with Sir Philip Green's excuses and empty promises.
"His answer throughout our inquiry was always that he was going to 'sort' the disastrous position he left the pension fund in when he sold off BHS to Dominic Chappell for £1.
"We are glad to see TPR (the Pensions Regulator) is now calling his bluff and instigating enforcement proceedings.
"It seems clear Sir Philip would rather kick the can down the road and avoid responsibility than come up with any fair, sustainable settlement for BHS pensioners."