Same-sex couples are discriminated against when searching for housing in online rental markets across the country, according to a new U.S. Department of Housing and Urban Development study released Tuesday.

In states like Maryland where such discrimination is illegal, the discrimination is even more pronounced, the study noted.

The HUD study, described by the federal agency as "the first-ever national study examining housing discrimination against same-sex couples in the private rental market," involved the authors sending 7,000 emails to housing providers, allegedly from prospective heterosexual and same-sex couples, and then comparing the responses received.

The results showed that same-sex couples experience unequal treatment from providers in metropolitan markets across the country -- primarily through receiving fewer responses to the emailed inquiries -- and that gay couples experience more discrimination than lesbian couples.

Discrimination based on sexual orientation is not explicitely prohibited by the Fair Housing Act, but HUD officials under the Obama Administration has been pushing to restrict such discrimination anyway.

On Feb. 3, the agency issued a new rule prohibiting all HUD-funded and HUD-insured housing providers from discriminating based on sexual orientation, gender identity and marital status.

In addition, 20 states -- including Maryland -- as well as Washington, D.C. and more than 150 localities have laws banning such discrimination.

But in a surprise finding, the study results showed that "slightly more adverse treatment" of same-sex couples was found in states with such protections.

The study, conducted between June and October of 2011 by HUD and the University at Albany in New York, shows the discrimination was present in every market tested. (Polls have shown increased acceptance of same-sex marriage, in Maryland and nationally, since then.)

In a statement, Bryan Greene, HUD's acting secretary for fair housing and equal opportunity, said the federal agency "is committed to making sure that [lesbian, gay, bisexual and transgender] individuals have access to housing opportunities."

More studies will follow, the agency said.

You can take a look at the study here.