A group of shareholders has launched a proxy fight to get their candidates elected to the board of Zim Integrated Shipping Services after the ocean carrier rejected an initial buyout offer from its chief executive as too low and continues to review other potential bids.

The Israel-based ocean carrier said in a statement Tuesday that a proxy advisor recommended shareholders reelect eight current board members at the company’s Dec. 26 annual meeting. The advisor also recommended that Zim shareholders vote against a slate of three directors nominated by an investor group that “made no attempt to work constructively with the board nor provided any suggestions for improving the company’s business or any other insight into how to create long-term value for shareholders,” Zim said.

The investor group — Mor Gemel & Pension Ltd., Reading Capital Ltd., and Sparta 24 — said in a letter nominating its candidates that it holds 5% of the company’s stock, Zim said. The investor group did not release the required stock exchange disclosures or a public statement about its proxy fight. There was no contact information available for the investors.

The investor group put up their nominees after a report that Zim Chief Executive Eli Glickman made a buyout offer that was less than the company’s cash balance, Zim said in its statement. While Zim evaluated Glickman’s proposal, it “unanimously determined that it materially undervalued the company,” the carrier said.

“The rumor that the board was willing to accept such an undervalued bid was clearly false,” Zim said.

The investor group wants the company to issue a special dividend, Zim said, which would undermine Zim’s “liquidity and create substantial risk to shareholder value given our charter-intensive model, which requires adequate cash to navigate industry cycles.”

Zim’s board said that it’s continuing a review of strategic alternatives that could include a merger or other another transaction. As part of that review, Zim has set up a transaction committee and appointed two additional outside directors to review any offers.