The Obama administration on Friday asked the US supreme court to rule that states cannot ban gay marriage.

The Justice Department filed a friend-of-the-court brief in four cases in which the court is due to hear oral arguments on 28 April.

“These facially discriminatory laws impose concrete harms on same-sex couples and send the inescapable message that same-sex couples and their children are second-class families, unworthy of the recognition and benefits that opposite-sex couples take for granted,” the solicitor general, Donald Verrilli, wrote in the brief.

Although the administration has been supportive of gay marriage, the brief marks the first time it has explicitly asked the supreme court to rule that bans violate the US constitution.

The justices are to consider whether same-sex marriage bans are prohibited by the constitution’s guarantee of equal protection under the law.

The nine justices will hear an extended 2-1/2-hour argument in cases concerning same-sex marriage bans in Ohio, Michigan, Kentucky and Tennessee. A decision is due by the end of June.

There are currently 37 states where gay marriage has been allowed to proceed, although a legal battle is ongoing in Alabama, with the state’s top court putting it on hold.

Dozens of briefs backing gay marriage were filed ahead of Friday’s deadline, including one signed by corporations such as Google Inc, American Airlines Group Inc, Goldman Sachs Group Inc and Johnson & Johnson.

Another was filed on behalf of dozens of prominent conservatives, including the former Republican National Committee chairman Ken Mehlman and David Koch, one of the billionaire Koch brothers known for donating to right-leaning political causes.

Opponents of gay marriage are not due to file their briefs until later in March.