A Hong Kong-based activist investment fund said Toshiba Corp's chip unit was worth as much as $40 billion, double the sale price agreed with a Bain-led consortium, as it escalated its opposition to the deal.

Argyle Street Management is seeking to persuade Toshiba to either negotiate a higher price or list the unit, highlighting concerns that the Japanese conglomerate agreed to sell it too cheaply while in the throes of a financial crisis last year.

The fund, which has $1.3 billion under management, says other activist investors are on its side, but it is not clear how much support it has garnered. Argyle has also not disclosed the size of its stake in Toshiba. Toshiba Memory, the world's No. 2 producer of NAND chips, is due to be sold for 2 trillion yen ($18.6 billion).