A third U.S. medical association says Defense Secretary Jim Mattis is mischaracterizing existing research to justify a partial ban on transgender troops in the military.

The head of the American Medical Association wrote to Mattis this week saying it believes there is “no medically valid reason” for excluding from service transgender people and those who are diagnosed with gender dysphoria, a medical condition that describes unhappiness or anxiety with a person’s current gender.

The Pentagon and White House have “mischaracterized and rejected the wide body of peer-reviewed research on the effectiveness of transgender medical care,” James Madara, CEO of the American Medical Association, wrote in a letter on Wednesday. “We believe there is no medically valid reason — including a diagnosis of gender dysphoria — to exclude transgender individuals from military service.”

The association disagrees with a central conclusion of a 44-page review and policy recommendation by Mattis that available research shows the effectiveness of treatment for gender dysphoria is uncertain.

The American Psychiatric Association and American Psychological Association have also questioned the conclusions of Mattis’ review and criticized his policy as discriminatory.

President Trump signed off last month on the Pentagon's proposal to bar people who are diagnosed with gender dysphoria or received treatment such as hormone therapy and surgery from enlisting in the military. Troops diagnosed with the condition could stay as long as they do not need such treatment.

Mattis also cited the cost of treatment, along with long recovery times, as a reason for the exclusion. But the AMA called it “negligible and a rounding error in the defense budget.”

The policy is currently on hold as the Trump administration battles transgender troops and rights groups in four federal court cases. Judges have granted injunctions in each case that block any change of policy while the cases are being heard.