Washington (CNN) -- Some 58 years after President Truman signed a bill proclaiming a National Day of Prayer, Thursday's observance may be one of the last to be officially recognized by Washington.
A federal judge declared the law unconstitutional last month, but the Justice Department is appealing the case on behalf of the White House.
U.S. District Court Judge Barbara Crabb in Wisconsin ruled on April 15 that the 1952 law creating the National Day of Prayer violates the ban on government-backed religion.
"[I]ts sole purpose is to encourage all citizens to engage in prayer, an inherently religious exercise that serves no secular function," Crabb wrote in the ruling. "In this instance, the government has taken sides on a matter that must be left to individual conscience."
The injunction against the National Day of Prayer will not take effect until the defendants in the case, President Obama and White House press secretary Robert Gibbs, exhaust their appeals, according to the decision.
The lawsuit against the Obama administration was brought by the Freedom From Religion Foundation, a group based in Madison, Wisconsin.
The president issued his proclamation for this year's observance less than three weeks after the judge's ruling, but he has not announced any plans to take part in any events.
"I call upon the citizens of our nation to pray, or otherwise give thanks, in accordance with their own faiths and consciences, for our many freedoms and blessings, and I invite all people of faith to join me in asking for God's continued guidance, grace, and protection as we meet the challenges before us," Obama said in his official proclamation.