UPDATE 1-Western Digital seeks court injunction to block sale of Toshiba chip unit


* Seeks injuction with California court

* Has been pursuing arbitration case

* Argues sale cannot be made without its consent (Adds comment from Western Digital CEO)

TOKYO, June 15 (Reuters) - Western Digital Corp said it has sought a court injunction that would prevent Toshiba Corp from selling its NAND chip business until its arbitration case against the Japanese conglomerate has been decided.

Western Digital, which jointly operates Toshiba's main chip plant, wants to buy the highly prized semiconductor unit and has been at loggerheads with the Japanese firm over an auction that could see the unit end up with a rival company.

In May, the California-based firm sought international arbitration arguing that Toshiba needs its consent for any sale and that Toshiba has breached their joint venture contracts by entertaining outside bids.

Toshiba's "attempts to circumvent our contractual rights have left us with no choice but to take this action, Western Digital's Chief Executive Steve Milligan said in a statement.

"Left unchecked, Toshiba would pursue a course that clearly violates these rights," he added.

The injunction is being sought in the Superior Court of California.

Toshiba declined to make immediate comment.

Toshiba wants at least $18 billion for the chip business and hopes to complete the deal as quickly as possible to help cover billions of dollars in cost overruns at its now-bankrupt Westinghouse nuclear unit.

It had been aiming to pick a preferred bidder for the business by Thursday but is now unlikely to come to a decision just yet due to last minute jockeying by suitors, a source familiar with the matter has said.

(Reporting by Makiko Yamazaki; Writing by Tim Kelly; Editing by Edwina Gibbs)