Nesting birds: Protected?

Just wondering, as I recently watched as maintenance workers felled a dead 
pine tree on the golf course.  This tree was adjacent to my backyard, and 
was a favorite for several species of woodpeckers.  For years they were 
hollowing out holes, probably for their nests.  And...since this is
nesting 
season, I know the workers did not check to see if there were any live 
nests.  Isn't there a written law or is it just "Law of the Jungle" that
you 
don't interfere with nesting birds of any species?  (except house
sparrows). 
A similar situation exists in my neighbor's backyard.  A dead hard wood
tree 
has nesting Great Crested Flycatchers in it. And at times the Red-bellied 
Woodpeckers use it nests.