The other answer suggested taking action like checking if you can get him fired if there is a clause that says "Don't say anything about your comany" or going to HR.

As such ratings are editable by the person that posted them, i would suggest that you go to the person, and ask what's wrong. What problems he has with the company and how to improve in his eyes. This might give some valuable insight.

I would not try to force a better rating, but rather improve to naturally get people more satisfied and this way they WILL give better ratings. Improving the working environment is always a good thing.

As a other answer said..

"If not then talk to the person and explain to them that it is not their private business but may have negative professional consequences."

..is imho maybe true but morally not the right thing to do. Every person has his own opinion and is allowed to have. If i was in a company that treats me not good or has other problems that might really frustrate me i would do the same.

The other answer suggested taking action like checking if you can get him fired if there is a clause that says "Don't say anything about your company" or going to HR.

As such ratings are editable by the person that posted them, I would suggest that you go to the person, and ask what's wrong. What problems he has with the company and how to improve in his eyes. This might give some valuable insight.

I would not try to force a better rating, but rather improve to naturally get people more satisfied and this way they WILL give better ratings. Improving the working environment is always a good thing.

As a other answer said..

"If not then talk to the person and explain to them that it is not their private business but may have negative professional consequences."

..is in my opinion maybe true but morally not the right thing to do. Every person has his own opinion and is allowed to have. If I was in a company that doesn't treat me well or has other problems that might really frustrate me I would do the same.