“There is no medically valid reason — including a diagnosis of gender dysphoria — to exclude transgender individuals from military service," American Medical Association CEO Dr. James Madara wrote in a letter addressed to Defense Secretary Jim Mattis.

The letter, sent Tuesday on behalf of "physician and medical student members" of the AMA, the nation's largest association of physicians, comes less than two weeks after the Trump administration released an order banning most transgender troops from serving in the military except under "limited circumstances."

"The accession or retention of individuals with a history or diagnosis of gender dysphoria — those who may require substantial medical treatment, including through medical drugs or surgery — presents considerable risk to military effectiveness and lethality," the White House said in a statement.

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Madara's letter asserted that the White House and the Defense Department "mischaracterized and rejected the wide body of peer-reviewed research on the effectiveness of transgender medical care," and it pushed back against claims that transgender service members would burden the military with "tremendous medical costs."

"The financial cost is negligible and a rounding error in the defense budget," Madara wrote. "It should not be used as a reason to deny patriotic Americans an opportunity to serve their country. We should be honoring their service."

Navy Lt. Cmdr. Blake Dremann, a transgender service member and the president of LGBTQ military advocacy group SPART*A, applauded the AMA's support for transgender people serving openly in the military.

"We are doing our jobs, deploying when called upon to do so and are medically capable," Dremann told NBC News. "We understand the high standards for military service. Our medically necessary treatment does not degrade from the needs or requirements from our services as emphasized by the AMA. We are showing that each and every day and will continue to do so."

This week's letter to Secretary Mattis is not the first time the AMA has opposed President Trump's transgender military ban. When the president first called for a ban in a series of unexpected tweets back in July, the organization swiftly released a public statement in opposition.

The administration of former President Barack Obama lifted the ban on transgender troops serving openly in June 2016. Following President Trump's policy reversal in July, a series of federal lawsuits have been filed in an attempt to block the ban. As a result of these lawsuits, multiple federal courts have issued temporary injunctions, preventing the ban from going into effect.

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