(CNN) -- The Obama administration will fight to preserve the law establishing an annual National Day of Prayer, the Justice Department confirmed Thursday.

A federal judge declared the law unconstitutional last week.

The Justice Department's official filing of a "notice to appeal" Thursday came as no surprise, after White House spokesman Matt Lehrich said following the ruling that President Obama intends to recognize this year's National Day of Prayer, which is May 6.

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.

The ruling produced predictable reactions, with most religious groups sharply criticizing it and groups backing a strict separation of church and state applauding it.

The injunction against the National Day of Prayer would not take effect until the appeals have been exhausted.

The case is Freedom From Religion v. President Barack Obama, White House Press Secretary Robert Gibbs, and Wisconsin Gov. Jim Doyle.