Wisconsin Democrats on Thursday announced a legislative effort that seeks to repeal the state's ban on gay marriage.

Flanked by marriage equality advocates, Rep. JoCasta Zamarripa and Senator Tim Carpenter, both Democrats, announced the effort at the state Capitol in Madison.

A majority (59%) of voters in 2006 approved a constitutional amendment which defines marriage as a heterosexual union. Wisconsin law also makes it a crime for gay couples to legally marry in another state. Neighboring states Iowa, Minnesota and Illinois have legalized same-sex marriage.

All 15 Senate Democrats are backing the proposed legislation, which faces an uphill battle in the Republican-led Wisconsin Legislature.

While Republican Governor Scott Walker's signature is not needed for the question to reach voters, he has strongly voiced his opposition to marriage equality.

(Related: Scott Walker calls gay marriage ban part of “healthy balance” of LGBT rights.)

Wisconsin currently recognizes gay and lesbian couples with domestic partnerships, which offer couples access to some of the protections of marriage but are not recognized by the federal government.

“Repealing our ban and moving one step closer to allowing same-sex couples to join [in] marriage is critical to ensure that all families are treated with dignity and respect,” Katie Belanger, president and CEO of Fair Wisconsin, the state's largest LGBT rights advocate, said during Thursday's press conference.

The announcement comes a week after four couples filed a federal lawsuit challenging the constitutionality of the state's ban.

(Related: Four couples challenge Wisconsin's gay marriage ban.)