Shareholders of Bermuda-based Aspen Insurance Holdings Ltd will ultimately decide whether Endurance Specialty Holdings Ltd’s hostile bid to take over their company will succeed — and on Friday both companies mailed out letters to them asking for their support.

Endurance, led by chairman and chief executive officer John Charman, is seeking to acquire Aspen in a cash and stock deal worth approximately $3.2 billion, but the Aspen board has vehemently rejected the offer.

On Friday, Aspen first announced that it had mailed a letter, urging shareholders to sign the enclosed blue revocation card to reject Endurance’s effort to convene a special meeting and its proposal for a scheme of arrangement that would force changes in the Aspen board.

Aspen’s move is in response to Endurance’s letter of June 18, which asks Aspen shareholders to show their support for Endurance’s proposals by signing a white authorisation and consent card.

In its letter, Aspen describes Endurance’s offer as “highly unattractive” and claims that the proposals for a meeting and changes to the Aspen board amount to “coercive legal attempts” aimed at acquiring Aspen at “the lowest possible price”.

Aspen goes on to claim that more than $500 million in premiums would be lost as a result of the combination and the value of Endurance’s shares would be hit by the dilutive impact of issuing more shares as part of the deal. It argues that Aspen would be better off as a stand-alone company.

In its latest letter, Endurance claims that Aspen’s management and directors have “stuck their heads in the sand”, refusing to engage in talks on the proposal. and are “more interested in protecting their personal interests than creating value” for shareholders.

Endurance also claims there is a lack of alignment in the interests of shareholders and those of the board and management — with insiders owning less than 1.2 percent of Aspen.

The letter also claims: “At the direction of current management, Aspen has acquired over 200 works of art — an unnecessary and wasteful diversion of management’s time and corporate assets.”

Endurance is targeting July 25 as the target date for Aspen shareholders to vote on its two proposals.