Hello that what i remember !

Jensen and Jeffrey dean morgan are members of a spaceship and doing some first contact and diplomatic missions.
They reach a planet where slavery is kinda the norm, Jensen must attend as the slave into the city as a sign of good wills.
Remember that the spaceship is landed near the city. Don't remember if Jared was in it.

It's so vague and old, like perhaps 5/7 years ago. I'm sorry.

I'm new here and i hope that i tagged well.

If it can help the fic was on a site with the description of the characters and i think there was some fanarts, one of them had Jensen with a collar.

found by walking_tornado
it's Sex Corps by Epeeblade
http://archiveofourown.org/series/710