Use of the Comma

Please settle a dispute about whether a comma belongs after the date in this sentence.

Reference is directed to your memorandum dated April 15, 2003 concerning security clearances for the security guard force at the Newark Division.

I don't think that a comma is necessary after the date. I realize that in most instances, it is advisable to insert a comma after a date. Such an example would be: On April 15, 2003, Headquarters forwarded a memorandum to the Newark Division concerning security clearances for the security guard force.

Please advise.

Thanks.