NEW YORK (TheStreet) -- Dollar Thrifty Automotive Group (DTG) appears to be growing impatient with its suitors.

The car rental holding company Sunday said it sent a letter to

Hertz Global

(HTZ) - Get Hertz Global Holdings, Inc. Report


Avis Budget

(CAR) - Get Avis Budget Group, Inc. Report

asking them to submit their "best and final definitive proposals" on potential mergers by October.

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a news release

, Dollar Thrifty's CEO, Scott Thompson, said that continuing uncertainty over a transaction was in "no one's best interest."

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"Hertz and Avis have made substantial progress with respect to regulatory reviews, and our Board has concluded that the time has come to determine if, and on what terms, a transaction can be achieved," Thompson added.

Hertz and Avis have been locked in a drawn-out bidding war over Dollar Thrifty.

Shares of Dollar Thrifty ended Friday down $2.46 at $61.91. Shares of Hertz ended the session down 48 cents at $9.71, and shares of Avis Budget finished the session down 12 cents at $11.61.

This article was written by a staff member of TheStreet.