More than 20,000 wedding dresses and hundreds of pairs of shoes are being sold following the collapse of bridal firm Berketex Bride.
The company ceased trading last month after 50 years.
Nottingham-based John Pye Auctions said it had reunited customers who had paid in full, or made a deposit, with their dresses and those remaining would go under the hammer.
The sale at John Pye's Port Talbot branch starts later.
It will continue every Friday and Saturday until further notice.
About 300 brides were left without a dress for their big day when the chain collapsed.
Vicky Morgan, 29, said she was "disgusted and desperately disappointed" after being told it was unlikely she would be able to collect her dress as it was in process rather than finished.
Trevor Palethorpe, from John Pye Auctions, said the firm was "expecting a great deal of interest in this sale due to the high-profile nature of this administration".
"There is an opportunity for brides to purchase a wedding gown at a fraction of the recommended retail price and walk away with it the same day," he added.