Western Digital Corp. is asking Apple Inc. to join its bid for Toshiba Corp.'s chip unit, sources said Wednesday, in an apparent effort to raise more cash for the purchase.

The Western Digital group is aiming to raise Toshiba's ¥2 trillion ($18 billion) asking price for Toshiba Memory Corp.

Western Digital, a key member of the consortium, has proposed a reduction in its share of investment in an effort to speed up antitrust screenings in Japan and abroad, and it could even decide to make no investment, sources have said.