NEW YORK ( TheStreet) -- Avis Budget Group ( CAP) is making a bid for Dollar Thrifty Automotive Group ( DTG), offering a 17% premium over an existing offer from Hertz Global Holdings ( HTZ). The Avis offers is for $46.50 per share of Dollar Thrifty. Yesterday, Avis amended a credit facility to secure financing for the Dollar Thrifty offer, and said that it expected to make a "substantially higher bid" for the company. Dollar Thrifty has already signed a merger agreement with Hertz. In a letter to Dollar Thrifty on Wednesday, Avis Budget management said, "We believe that the higher purchase price we are offering, combined with the terms of our proposed merger agreement, makes our offer a superior one from the perspective of Dollar Thrifty and its shareholders. Hertz should be required to agree to accept these provisions as a condition to Dollar Thrifty permitting Hertz to continue to make offers for the company." Reuters had reported on Tuesday that Avis was amending its JP Morgan-led credit facility and was seeking to increase the maximum amount of first-lien senior secured debt to $2 billion from $1.5 billion. Dollar Thrifty shares were down more than 2% in after-hours trading, while Avis and Hertz shares were unchanged. -- Written by Eric Rosenbaum from New York. Follow TheStreet.com on Twitter and become a fan on Facebook.