FILE PHOTO: The logo of Toshiba Corp is seen as window cleaners work on the company's headquarters in Tokyo, Japan, February 14, 2017. REUTERS/Toru Hanai/File Photo

TOKYO (Reuters) - Toshiba Corp said on Thursday it would invest in a new memory chip production line without joint venture partner Western Digital Corp, in a counter-punch against the U.S. firm which has opposed a planned auction of the business.

The Japanese conglomerate has been trying to sell the unit to plug a balance sheet hole left by its failed U.S. nuclear business. Western Digital, which says any deal would require its consent, has opposed Toshiba’s pick of a preferred bidder and has put in a competing offer.

Toshiba said it would invest 195 billion yen ($1.76 billion) in the Fab 6 production line in Yokkaichi, central Japan, up by 15 billion yen from its original estimate, because it would now go it alone.

Western Digital said in a statement that it was disappointed by Toshiba’s decision and that it too was determined to invest in the upgrade.

Their prolonged fight has unnerved members of the preferred bidder group, which includes Japanese state-backed funds, private equity firm Bain Capital and South Korean chipmaker SK Hynix Inc. The Japanese funds are asking that Toshiba resolve the conflict before the $18 billion deal.

Toshiba shut out Western Digital employees from databases at their memory chip joint venture in late June as tensions around the auction escalated. It temporarily suspended the lockout in July following a restraining order by the Superior Court of California, but reinstated it a week later as its petition for an appeal was accepted.

Toshiba on Thursday said it would allow Western Digital employees to access the databases, a day after a U.S. court ordered it to do so. But the firm said in a statement it is just “a proceeding with many rounds and many rulings.”

A Toshiba spokesman said that despite its latest decision to invest in the upgrade alone, it was open to talks with Western Digital about later plans.

The new line, set to start operating around next summer, will produce memory chips using next-generation three-dimensional technology as Toshiba aims to raise the 3D proportion to about 90 percent in the year ending in March 2019.