UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No.      )

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¨ Preliminary Proxy Statement

¨ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

¨ Definitive Proxy Statement

x  Definitive Additional Materials

¨ Soliciting Material Pursuant to §240.14a-12

USF Corporation

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

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Filed by: USF Corporation

Pursuant to Rule 14a-6

under the Securities Exchange Act of 1934

Subject Company: USF Corporation

Commission File No. 0-19791

On May 7, 2005, the mailing of an updated proxy statement/prospectus to USF stockholders was commenced. USF included in the mailing a letter from Paul J. Liska, Executive Chairman of the USF Board of Directors. A copy of the letter is set forth below.

Additional Information. Yellow Roadway and USF commenced the mailing of an updated proxy statement/prospectus to USF stockholders on May 7, 2005. A copy of the updated proxy statement/prospectus was filed by Yellow Roadway with the SEC on May 6, 2005. Investors are urged to read the updated proxy statement/prospectus because it contains important information. Additional information concerning the amended merger may be filed with the SEC and investors are urged to reach any such materials as well. You will be able to obtain the documents free of charge at the website maintained by the SEC at www.sec.gov. In addition, you may obtain documents filed with the SEC by Yellow Roadway free of charge by requesting them in writing from Yellow Roadway or by telephone at (913) 696-6100. You may obtain documents filed with the SEC by USF free of charge by requesting them in writing from USF or by telephone at (773) 824-1000.

Participants in the Solicitation. USF, and its directors and executive officers, may be deemed to be participants in the solicitation of proxies from the stockholders of USF in connection with the acquisition. Information about the directors and executive officers of USF and their ownership of USF stock is set forth in the USF Annual Report on Form 10-K for the year ended December 31, 2004. Investors may obtain additional information regarding the interests of such participants by reading the updated proxy statement/prospectus filed with the SEC in connection with the amended merger.

Dear Fellow USF Stockholder:

On May 2, 2005, USF and Yellow Roadway announced that the companies had amended the Agreement and Plan of Merger, dated February 27, 2005. In connection with the amendment, we have updated our April 22, 2005 Proxy Statement/Prospectus (which we refer to as the original proxy statement/prospectus) and we enclose a copy of the updated proxy statement/prospectus, dated May 6, 2005. We urge you to read this document carefully.

The principal changes in the amended merger agreement from the original merger agreement are the following:

· The portion of the total merger consideration payable as cash has been increased from approximately 50% to approximately 65% and the portion payable in shares of Yellow Roadway common stock has been reduced from approximately 50% to approximately 35%.

· The cash election right has been eliminated so that all shares of USF common stock (excluding those owned directly or indirectly by USF or Yellow Roadway or by any stockholder validly exercising appraisal rights) will be cancelled at the effective time of the amended merger and converted into a right to receive:

· $29.25 in cash (representing 65% of the original merger agreement’s $45.00 cash election merger consideration), and

· 0.31584 shares of Yellow Roadway common stock (representing 35% of the original merger agreement’s 0.9024 stock exchange ratio).

Under the terms of the original merger agreement, 50% of the shares of USF common stock would have been converted into $45.00 cash and 50% of the shares of USF common stock would have been converted into 0.9024 shares of Yellow Roadway common stock (subject to adjustment). Assuming all stockholders elected to receive 50% cash and 50% Yellow Roadway common stock, each stockholder would have received $22.50 per share in cash and 0.4512 shares of Yellow Roadway common stock.

· U.S. holders of USF shares should recognize gain or loss for U.S. federal income tax purposes equal to the difference, if any, between their amount realized (the fair market value of Yellow Roadway shares plus the amount of cash received as merger consideration) and their adjusted tax basis in their USF shares. Under the terms of the original merger agreement, this taxable gain would have been recognized only to the extent the U.S. holder received cash in the merger in an amount equal to or lesser than the gain in the shares exchanged by the U.S. holder in the merger.

· The structure of the merger has been modified so that a wholly owned subsidiary of Yellow Roadway will merge with and into USF, with USF as the surviving entity. Upon consummation of the amended merger, USF will become a wholly owned subsidiary of Yellow Roadway.

· Several of the conditions to closing in the original merger agreement have been modified to give greater certainty that the transaction will be completed.

· Several of the provisions concerning the companies’ rights to terminate the original merger agreement and obligations to pay a termination fee under certain circumstances have been modified to reflect the modified closing conditions.

Please note that:

· The USF special stockholder meeting to vote on the amended merger agreement will still be held on May 23, 2005 and the record date for the special meeting remains April 21, 2005.

· USF will not vote any proxies received on the white proxy card included in the original proxy statement/prospectus or received by internet or telephone pursuant to the instructions in the original proxy statement/prospectus.

· If you want your proxy to be counted at the special meeting, you will need to use the new BLUE proxy card that is included with the enclosed proxy statement/ prospectus. Alternatively, you may also submit a proxy by internet or telephone by following the directions provided on such card or in the enclosed proxy statement/prospectus under the heading “Voting by Proxy – How to Vote,” on page 36.

· If you have any questions regarding the enclosed proxy statement/prospectus or how to submit a proxy or if you need additional copies of the materials, please contact Morrow & Co., Inc., our information agent and proxy solicitor, by telephone toll-free at (800) 607-0088.

Whether or not you plan to attend the USF special stockholder meeting, please take time to vote by using the new BLUE proxy card included with the enclosed proxy statement/prospectus. You may also submit a proxy by internet or telephone in accordance with the directions provided on such card or the directions provided within the enclosed proxy statement/prospectus. YOUR VOTE IS VERY IMPORTANT.

THE BOARD OF DIRECTORS OF USF CORPORATION HAS UNANIMOUSLY APPROVED THE AMENDED MERGER AGREEMENT, HAS UNANIMOUSLY DETERMINED THAT THE AMENDED MERGER AGREEMENT IS ADVISABLE AND UNANIMOUSLY RECOMMENDS THAT USF STOCKHOLDERS VOTE FOR ADOPTION OF THE AMENDED MERGER AGREEMENT.

On behalf of USF, I thank you in advance for your support.

Very truly yours,

/s/ Paul J. Liska

Paul J. Liska

Executive Chairman of the Board of

Directors of USF Corporation

May 6, 2005