This will be the second straight year the family and related parties, which together hold 33.92 percent of Idemitsu shares, will oppose the re-election of Chief Executive Officer Takashi Tsukioka, and other board members, at Idemitsu's annual general shareholders' meeting.

Idemitsu's management has been looking at various options to complete the merger but none of them have swayed the founding family.

The family came close to removing Tsukioka, along with other board members, at last year's shareholders' meeting.

Idemitsu Kosan completed the purchase of just under one-third of Showa Shell last December. The goal of combining the two companies has been delayed indefinitely due to the founding family's opposition.

The family plans to send letters to other shareholders to vote against electing five of the 12 board candidates, according to its new lawyer Yohei Tsuruma.

"(Idemitsu) should not integrate operations (with Showa Shell) but act alone," Tsuruma said at a news conference.

The family will take legal action against Idemitsu if the company decides to issue shares to a third party to try to dilute the family's shareholding, he added.

Tsuruma also said he would represent the family at the Idemitsu's shareholders' meeting scheduled for June 29.

(Reporting by Osamu Tsukimori and Taiga Uranaka; Editing by Christian Schmollinger)

Stocks treated in this article : Showa Shell Sekiyu KK, Idemitsu Kosan Co., Ltd.