First, you will have to wonder why are you under-assigning tasks to your employees and after that you will need a management system to keep track of what does each of them.
OK, you're starting to ruffle some feathers here now.
Let me give you a dose of the "Real world".
US Steel has installed GPS trackers on their production trucks. These trucks don't get stolen, they carry something like 260 tons of rock in a single trip. The reason for the GPS tracking is to make sure that they keep moving, because the drivers would pull off and take a nap.
The management system HAS been installed there. By your arguments, shouldn't they be allowed to pull over, pull out their laptop (or go use a company's laptop) and get on Facebook for a little while each day, or each trip?
The owner of the company that I work at now has asked me to either monitor or completely block Internet access from the laboratory.
The bottom line is, YES. You work for the company, YES, they can tell you whether or not you can use the Internet for personal use, and YES, they will be more than happy to show you the door if it becomes a problem.
Other than wages, sick time, and so forth you have no "Rights" as an employee. You do not have the "Right" to check your Facebook. You do not have the "Right" to use the phone for personal calls. You do not even have the "Right" to be treated fairly, without fear of nepotism or a butt-kissing "Yes" man getting promoted before you.
You DO have the right to do a good job, to get a paycheck, so you can pay for your home, groceries, and so forth. You have the right, through your hard work, to keep yourself from being homeless (hopefully).
Now I'll step off of my soap box; I have to leave for work. Because *I* realize that like a MAJORITY of Americans, I'm about 2 paychecks away from being homeless; I *NEED* my job in order to survive and not be on the soup line. And if that means I have to wait until I get home to tweet, so be it.
Just my 2¢
"What the captain doesn't realize is that we've secretly replaced his Dilithium Crystals with new Folger's Crystals."
--Greg