Legal advice: paying back paychecks

Our baby was born 18 months ago and SO took family paid leave (75%) for about 1 month. Since that time he was getting paid about .60 cents extra that he supposedly shouldnt of and they added it up to $500. Now they want him to pay it back. He works a major corporate store which i will not name but yea its huge. Does that sound right? He wants to call corporate to straighten this out but i just want to know what might happen. Anyone have advice or experience dealing with this. Thanks!