Western Digital Corp. said yesterday it will seek an injunction to block the sale of Toshiba Corp.’s prized semiconductor business to a rival group, upping the ante in an acrimonious battle with its chip venture partner.

The latest legal action by the US firm, which jointly invests in Toshiba’s main chip plant, comes in the wake of the Japanese conglomerate’s decision last week to sell the unit to a consortium led by Bain Capital LP and South Korean chipmaker SK Hynix.

The $18 billion agreement with the Bain group is, however, still unsigned, with Toshiba telling its main banks this week that Apple Inc., a member of the consortium and an important client, had yet to agree to key terms. Western Digital’s injunction is being sought with the International Court of Arbitration, where the California-based company, which argues no deal can be done without its consent, initiated proceedings against its partner earlier this year.

A panel of three arbitrators may be formed as early as this week and a decision on the injunction could come late this year before any deal closes, a source familiar with the matter said, declining to be identified due to the sensitivity of the matter. A final ruling on the dispute is not expected before 2019.

The contentious auction has underscored how high the stakes are, as rival suitors, the Japanese government and Toshiba’s creditor banks all squabble over the world’s second biggest producer of NAND memory chips.

For Toshiba, a signed deal would come not a moment too soon as it needs to raise billions of dollars to cover liabilities arising from its now bankrupt US nuclear unit Westinghouse before the end of the financial year in March. If it fails to do that, it could be delisted.

Even if Toshiba manages to sign the deal with the Bain group imminently, it is still cutting it fine as regulatory reviews usually take at least six months.

Western Digital said in a statement that Toshiba’s decision had been disappointing, given that it had made major concessions. These included giving up its participation in the consortium it was part of, leaving KKR/INCJ and a state-backed fund, the Innovation Network of Japan (INCJ), as the main investors. It also gave up on a plan to take a future equity stake. It said it was vehemently opposed to a Bain deal, arguing that the inclusion of SK Hynix, a rival chipmaker, heightens the risk of technology leaks and introduces the risk that the deal may not clear regulatory reviews, unlike the KKR/INCJ bid which does not include a chipmaker.

Toshiba declined to comment.

Western Digital, one of the world’s leading makers of hard disk drives, paid some $16 billion last year to acquire SanDisk, Toshiba’s chip joint venture partner since 2000. It sees chips as a key pillar of growth and is desperate to keep the business out of the hands of rival chipmakers.

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