Washington (CNN) The largest association of doctors in the United States is arguing that there is "no medically valid reason" to bar transgender individuals from serving in the military, countering President Donald Trump's policy issued in March.

"We believe there is no medically valid reason -- including a diagnosis of gender dysphoria -- to exclude transgender individuals from military service," the American Medical Association wrote in a letter to Defense Secretary James Mattis dated Tuesday.

"Transgender individuals have served, and continue to serve, our country with honor, and we believe they should be allowed to continue doing so."

The letter, signed by AMA CEO James Madara, argues that Mattis' recommendations to the President "mischaracterized and rejected the wide body of peer-reviewed research on the effectiveness of transgender medical care."

The letter was first reported by Politico.

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