Is it illegal to install video surveillance of employees without their consent?

Question Details:

We recently put up a still shot camera outside of our building at work that takes a picture of the door (motion activated). We have had a large number of thefts and therefore, did not inform employees of the camera. One of the employees noticed the camera and brought it to our attention (that it is illegal to have the camera without notifying employees). Is this accurate? And if we install video surveillance inside of the building (which we are planning on), must we notify employees and/or customers of this as well? In MA. Important Notice