WASHINGTON (Reuters) - President Joe Biden issued a proclamation on Wednesday that would set in motion a process to pardon U.S. veterans convicted by the military for gay sex, which was illegal until the provision was repealed in late 2013.

The Biden administration estimates that the proclamation could affect thousands of individuals convicted of consensual sexual conduct and who may be eligible for a pardon, senior administration officials said.

"Our Nation's service members stand on the frontlines of freedom, and risk their lives in order to defend our country," Biden said in a statement. "Despite their courage and great sacrifice, thousands of LGBTQI+ service members were forced out of the military because of their sexual orientation or gender identity."

The affected individuals can apply for proof that they may be eligible, and if they receive a certificate of pardon, they can then apply to have their discharge characterization changed, the officials said.

The administration is considering ways to reach out to individuals who might be eligible for the pardon, the officials said.

In late 2013, the U.S. Senate passed a measure that included a repeal of a military ban on consensual sex, defined in Article 125 of the Uniform Code of Military Justice as "unnatural carnal copulation," according to the ACLU. The Senate sent the measure to former President Barack Obama to sign.

Biden served under Obama as vice president.

(Reporting by Stephanie Kelly and Idrees Ali; Editing by Leslie Adler)

By Stephanie Kelly and Idrees Ali