It's an ad hominem attack if you are attempting to refute an argument they made for the pay raise.

For example, if a senator gave a speech detailing why senators needed more money and someone dismissed the arguments based on the senator's sentatorness rather the quality of the argument's themselves.

Also, an ad hominem is not merely a 'personal attack.' For example, an insult is not an ad hominem. An ad hominem is an attempt to discredit an argument based on qualities of the arguer instead of the argument itself. Pointing out a conflict of interest is an ad hominem attack if you are using it to discredit an argument.