UPDATE 1-Steel Partners opposes bid for Aderans stake

* Steel Partners opposes Unison's offer to buy Aderans shares

* Steel Partners says Unison's offer is below book value

* Aderans to hold shareholders meeting on May 28

TOKYO, May 11 (Reuters) - U.S. hedge fund Steel Partners said it has urged shareholders of loss-making wig maker Aderans Holdings (8170.T) to reject an offer by Japanese private equity fund Unison Capital to buy Aderans shares.

Japan's Aderans said last month it supported Unison Capital's bid for at least a 35 percent stake in Aderans to replace top shareholder Steel Partners, which has been pushing for management changes.

Unison Capital's proposed offer is "inadequate and coercive", Steel Partners said in a statement on Monday.

Unison Capital has said it will offer 1,000 yen per Aderans share in an offer running June 1-29, 4.5 percent higher than Monday's close of 955 yen. [ID:nT225880]

Steel Partners said the offer price was "significantly" below Aderans' book value per share of 1,582 yen as of Feb. 28.

The U.S. hedge fund said it has asked Aderans shareholders to vote against Aderans' candidates for the board, which include three Unison Capital officials, at an Aderans shareholders meeting on May 28.

Steel Partners said it has also asked stakeholders to reject Aderans' proposal to sell treasury stock to Unison Capital, saying such a move would dilute the value of shares.

Aderans has said it will sell its own stock, equivalent to 7 percent of its outstanding shares, to Unison Capital. (Reporting by Junko Fujita; Editing by Chris Gallagher)