can a workers comp settlement have a lien put against it for past due child support?

If it is the Deoartnent if child Support Services, you can expect that agency has wide enforcement powers.  You can contact the Department and ask to know the authority for taking such actions and whether you can file for an exemption from it.  If is is by a private attorney, you need one or you need to see the Family Law Facilitator at your local courthouse for advice, which is both from a lawyer and free to you.