[Hampshire] Sudo question

I wonder if anyone could explain this to me?

In my sudoers file I have:-

%users ALL=NOPASSWD: /usr/sbin/pm-suspend

but if I run "pm-suspend" I am told this can be only run by root, and if
I run sudo pm-suspend I am asked for my password. I assume that there
must be something wrong with the line above from /etc/sudoers, but my
research hasn't thrown up an answer.

Grateful as ever for any help

Owain