I'm suprised nobody mentioned this, but you really should be untainting your data in addition to checking that it exists. That way if someone puts erroneous data in to your employee number, you'll catch it before it potentially causes any damage. Do a perldoc taint for further reading.

And as other Monks have mentioned, you really should look at using the param method of CGI.pm. It makes life a lot easier when doing this type of thing.