A top Dollar Thrifty shareholder intends to vote against a merger deal with Hertz Global Holdings Inc., according to the Wall Street Journal.

Paul Reeder, president of Boston hedge fund PAR Capital Management Inc., said Hertz's cash-and-stock offer undervalues his holdings. PAR expressed opposition to a Hertz deal as far back as May.

Since then, Hertz has raised its offer 27 percent. But Reeder said he remains unmoved.

Reeder's views could be crucial to Hertz when the deal goes for a vote before Dollar Thrifty shareholders on Sept. 30. The offer must receive a majority of votes cast to win approval, and Dollar Thrifty might not secure that majority.

Hertz reiterated Sept. 28 that its latest offer remains its "best and final," after rival Avis Budget Group Inc. appealed to Dollar Thrifty shareholders to vote against the deal.

In April, Hertz Chief Executive Mark Frissora estimated the combination would generate cost savings of $180 million. RiskMetrics Group has estimated these synergies to be worth $900 million over time, about 70 percent of the total $1.3 billion enterprise value of Hertz's offer.