Can someone provide me with the internet address of the internet site in which employers can verify the social security numbers of their employees?

Just had a run in with the tile store next door that appears to be hiring illegals. I would assume they are illegal as they don't speak one word of english. I told him next time I saw those guys I was calling the police and ICE. He's trying to tell me that they satisfied his paperwork requirements but when I asked if he ran a check on their SS numbers, he drew a blank.

I want to be sure he does have the appropriate means in which to verify their legal status before I do call ICE.