Prominent conservative and family groups filed an amicus brief Wednesday against an earlier court ruling that deemed the National Day of Prayer unconstitutional.

"In her decision to strike down the National Day of Prayer, Judge Barbara Crabb attempted to undo two hundred years of American history," said Kelly Shackelford, president/CEO of Liberty Institute, which filed the brief on behalf of more than 30 groups and individuals.

"The decision below was an attack upon our heritage and the religious freedom upon which our nation was founded. This outrageous decision must be overturned."

Among those joining the challenge are James C. Dobson, founder of Focus on the Family; the Family Research Council; Focus on the Family Action; the American Civil Rights Union; Let Freedom Ring; and family policy councils from throughout the country.

"Prayer is the underpinning of this country that makes it great. I am proud to file this brief along with so many wonderful groups," said Dobson. "Our nation has a rich history of Presidential proclamations for prayer and thanksgiving, and we must not allow revisionist history to dilute that heritage and freedom."

In April, U.S. District Judge Barbara Crabb struck down the federal statute creating the National Day of Prayer, concluding that it connotes endorsement and encouragement of a particular religious exercise. A lawsuit had been filed in October 2008 by the Freedom From Religion Foundation.

Despite the ruling, religious groups were free to organize prayer events on the first Thursday of May. Still, some vowed to appeal the decision.

Liberty Institute argues in its brief that invalidating the annual day of prayer "would be an act of hostility to religion, not the accommodating neutrality required by the Establishment Clause."

Contending that it is "completely consistent with the First Amendment," the legal firm also notes that the prayer day "is a benign acknowledgement of the religious nature of the American people."

"Moreover, participation in this acknowledgement is entirely voluntary, and does not entail any person’s being subjected to unwelcome assertions of religious faith."

The annual prayer event was created in 1952 by a joint resolution of the United States Congress, and signed into law by President Harry S. Truman. Since then, all presidents, including President Obama, have issued proclamations designating the National Day of Prayer each year.