A number of large-city mayors in the US have formed a coalition with the hope to achieve same-sex marriage equality.

The group have joined together with a view to increasing the pressure on President Barack Obama and to achieve full support of equal marriage rights nationwide.

The combined effort has been organised by Freedom to Marry, a group campaigning for country-wide acceptance of gay marriage, and an end to ‘federal marriage discrimination.’

Freedom to Marry are planning to hold a press conference at 10am on Friday at the Capital Hilton Hotel, Washington DC, which 70 mayors are said to be attending.

The group released a statement: “By joining the group, mayors hope to expand public and political support for ending the exclusion of same-sex couples from marriage.”

The so-called ‘Bipartisan coalition’ includes Michael Bloomberg of New York, Rahm Emanuel of Chicago, and Annise Parker of Houston, and is chaired by mayors Jerry Sanders of San Diego, Thomas Menino of Boston and U.S. Conference of Mayors President Antonio Villaraigosa of Los Angeles.

Obama’s position on same-sex marriage rights has been unclear in the past. He has not supported same-sex marriage, rather than ‘civil union’ but he has also praised politicians in support of the change.

There is speculation that Obama will maintain his position until the Presidential election in November.