The US military has spent between $290 million and more than a half a billion dollars implementing its ban on open gay service, a new study released Tuesday found.

The research brief released by the Williams Institute at the UCLA School of Law, a public policy institute that focuses on sexual orientation law, also estimates that 66,000 gay, lesbian and bisexual people are currently serving in the Armed Forces, approximately 2.2% of all military personnel.

“Despite official policy requiring that lesbians, gay men and bisexuals remain silent about their sexual orientation, data from the US Census Bureau suggest that an estimated 66,000 LGB men and women are serving in the US military,” Dr. Gary J. Gates, who authored the study, said in a press release.

Congress approved the ban, also known as “don't ask, don't tell,” in 1993. It prohibits gay and lesbian service members from revealing their sexuality at the risk of losing their jobs.

During the presidential campaign Obama pledged to repeal the law. In October, he reiterated his promise at a fundraiser attended by roughly 3,000 gay activists, but offered no specifics.

The White House has confirmed that President Obama will discuss the ban during his State of the Union address on Wednesday.

The new study could provide powerful ammunition for activists lobbying for repeal of the ban.

“Ending 'don't ask, don't tell' will save a substantial amount of taxpayer dollars since estimates suggest that the policy has cost more than half a billion dollars,” Gates concluded.

The study also found that lifting the restrictions “could attract an estimated 36,700 men and women to active duty service and 12,000 more individuals to the guard and reserve.”