In short the artist placed the United States flag on the ground in front of a visitors book and asked the viewer to consider wether they could stand on the flag to write a comment. Public reaction to this work is all covered in his website. And there are a number of magazine and blogs on this peice easily found.
(The link is to an interview with him).
(A great precis on the piece- nice safe site)
Above is the work 'Piss Christ' by Andreas Serrano. A sculpture of Christ on the cross suspended in urine and photographed . Initially the piece attracted approval since the artist did not reveal what the crucifix was suspended in. Later, when people found out, the work was attacked, vandalised and subjected to censure by the church, church groups and local moralists. On April 17, 2011, a print of Piss Christ was vandalized "beyond repair" by Christian protesters while on display during the Je crois aux miracles (I believe in miracles) exhibition at the Collection Lambert, a contemporary art museum in Avignon, France. Serrano's photo The Church was similarly vanndalised in the attack.
Serrano himself has stated the work is more about the cheapening of the image of Christ in society, whatever your religious views, he was concerned more about the morality of having a man nailed to a cross being tortured being represented in gold and silver.
For parity here is an interview with famous art critic and celebrity Sister Wendy who defend the piece.
If you have thoughts on censorship of art please leave a comment you can do so anon if you wish. Or if you require any more info on these artists, i am more than happy to help.