Is it against copyright to show a movie at work?
Yes it is because it is a public viewing, you need the written
permission of the studio that produced it, or buy a license for
public viewing from the studio itself (But that costs quite a
lot)
As opposed to the original contributor's answer above, it
depends on who can view the movie. A "public viewing" is one that
is open to the public. However, if you show a movie at work and
those in attendance are all employees, it is then a "PRIVATE"
screening/viewing of the film.