National Day of Prayer

The President shall issue each year a proclamation designating the first Thursday in May as a National Day of Prayer on which the people of the United States may turn to God in prayer and meditation at churches, in groups, and as individuals.

This law was passed in 1952 as discussed here, which covers various aspects including recent controversy over it being sectarian in practice. It is a permanent establishment of days of prayer and thanksgiving that have a long history in this country.  Some answer this with a "day of reason" though (hard as it might be thought by some) there can be some overlap.  Note that a couple years after the establishment of this day, the U.S. Congress also added "under God" to the Pledge. 

President Obama has tried to be inclusive including a statement concerning how "we protect the fundamental right of all peoples to practice their faith how they choose, to change their faith, or to practice no faith at all, and to do so free from persecution and discrimination." It's useful, if you have this sort of thing, to use it in that sort of inclusive matter.  But, there is still a basic problematic aspect of singling out religious practice here. The possible problems of this sort of thing was recognized back to the days of Jefferson, including in the eyes of believers of God.

And, it is not even a day honoring free exercise of religion or even God.  This is a problem in itself -- everyone doesn't believe in God and having secular leaders provide statements of this sort is problematic. I guess "may" can be simply a statement of possibility ("may" do a lot of things), but some might rightly infer a bit more.  A certain type is singled out -- "turn to God in prayer and mediation" etc.  It is somewhat comparable to Wallace v. Jaffree where more than a moment of silence was involved, but singling out prayer for favoritism. And, private action comes within its terms but "churches" (a Christian connotation) is cited first.

I'd suggest a more inclusive day honoring free exercise of religion.