SALT LAKE CITY — Eighty-one members of the Utah State Legislature, including the House Speaker and Senate President, filed an amicus brief with a federal appeals court, supporting Utah’s Amendment 3.

The filing, made late Monday, was submitted in the names of 58 of the 75 sitting House members and 23 of the 29 members of the Utah Senate.

“We especially feel a profound duty to the children of the State, derived from deep historical roots and experience that confirm children are substantially benefited and best served by public endorsement and recognition of marriage as the legal union between a man and a woman as husband and wife,” the filing, written by attorney Robert Smith, states.

The filing declares that “states have a responsibility for domestic relations laws,” and the elected Utah State Legislature represents the “voice of the people.” In 2004, 66% of Utahns passed Amendment 3, which defines marriage as between a man and a woman and does not recognize anything else.

In December, a federal judge in Salt Lake City declared Amendment 3 unconstitutional, ruling that it violated gay and lesbian couples’ rights to due process and equal protection under the U.S. Constitution. For 17 days, more than 1,300 same-sex couples wed in the state until the U.S. Supreme Court granted Utah’s request for a stay pending appeal.

The 10th U.S. Circuit Court of Appeals in Denver has scheduled arguments in the case on April 10.

Changing Utah’s marriage definition, the amicus brief says, could affect numerous statutes in state law, with “unintended consequences.” The filing cites some of those impacts including birth and adoption laws, divorce, legal parenthood, education, premarital counseling, and even the state’s Utah Marriage Commission.

“The purposes of Utah’s marriage law are reasoned, principled, and consistent. It is rational—even compelling—for the laws of the State to reflect a consistent recognition, endorsement and promotion of husband-wife marriage as the proper and best institution for childbearing and childrearing and the perpetuation of an ordered society,” the lawmakers state in the brief.

The filing is one of more than a dozen “friend of the court” briefs submitted Monday in support of Utah’s defense of Amendment 3, including a number of individuals and:

16 Utah counties

The Eagle Forum

The Becket Fund for Religious Liberties

The Sutherland Institute

The Institute for Marriage and Public Policy

Concerned Women for America

The Center for Constitutional Jurisprudence and “27 scholars of federalism and judicial restraint.”

Parents and Friends of Ex-Gays and Gays

The National Association for Research and Therapy of Homosexuality

Liberty Counsel, Inc.

The states of Alabama, Alaska, Arizona, Colorado, Idaho, Indiana, Montana, Nebraska, Oklahoma and South Carolina

The state of Michigan

The Church of Jesus Christ of Latter-day Saints, the U.S. Conference of Catholic Bishops, the National Association of Evangelicals and the Lutheran Church-Missouri Synod also submitted an amicus brief on Monday.

Read that filing here.

The lawyers for three gay couples who sued, challenging Amendment 3 have until Feb. 25 to file their response to the Utah Attorney General’s first brief. Gay rights groups and others are expected to file their own amicus briefs in support around that time.