More than 80 Congressmen, in a letter to Defense Secretary Jim Mattis, are voicing opposition to "unacceptable" changes to the transferability policy for the Post 9/11 G.I. Bill.

Read the letter here.

Their message follows a July 12 DoD policy change that prohibits servicemembers with more than 16 years of service to transfer Post-9/11 GI Bill educational benefits to family members. This policy would take effect on July 12, 2019.

[Related: Big Changes to Post 9/11 G.I. Bill: What You Need To Know]

Last week, 83 members of Congress penned the letter to Mattis, demanding he reverse the policy changes.

“On behalf of a grateful nation, it is our collective duty and responsibility to uphold the hard-earned benefits of our nation's active-duty service members and veterans, and to remain faithful stewards of the GI Bill's educational assistance program,” the letter states.

The Post-9/11 G.I. Bill was implemented on Aug. 1, 2009 as a commitment to veterans that the government would provide them an education and opportunity in recognition of their service during war. The bill pays tuition and fees directly to the school in which the veteran is enrolled, and includes a monthly housing allowance, up to $1,000 annually, for books and supplies.

The transferability to a servicemember's spouse or children was created during the height of the war in Iraq and Afghanistan as a recruitment and retention tool.

The benefit is overseen by the DoD, but funded through Veterans Affairs. More than 773,000 veterans have used the GI Bill educational benefits, according to the VA.

“Revoking transferability benefits breaks this commitment with our most dedicated and seasoned service members,” according to the letter.

Under the policy change, Post-9/11 G.I. Bill educational benefits can only be transferred to family members for servicemembers with fewer than 16 years of service. Those with more than 16 years will be able to keep the educational benefit, but will be unable to transfer to family members.

All servicemembers must be eligible to be retained for four years from the date of their election to transfer benefits.

The servicemembers who are most likely to lose out in the change are those more senior officers and enlisted troops who cannot make the service commitment or those with hopes to marry and/or have kids who have not yet done so.

The policy affects all uniformed services, including the Coast Guard, U.S. Public Health Service and National Oceanic and Atmospheric Administration.

The change was announced after a thorough review of the policy, according to a spokeswoman from the Office of the Secretary of Defense's Accession Policy.

Rep. Jimmy Panetta, D-Calif., who deployed to Afghanistan during his time in the Navy Reserve, is among the members of Congress who signed the letter. He was a co-sponsor of the Forever GI Bill - and called the policy change “repugnant.”

“The post-9/11 GI Bill represents our commitment to recognizing the sacrifice of our veterans and empowering them as they tackle new challenges, careers, and ways of continuing to contribute to our country and communities after their service,” Panetta said in a statement. “Removing already-earned benefits breaks faith with our servicemembers, sends the wrong message to those considering a military career and sets a bad precedent for the removal of other benefits on the eve of retirement.”

Amanda Dolasinski is MOAA's staff writer. She can be reached at amandad@moaa.org. Follow her on Twitter @AmandaMOAA.