Validate Fields When A Dynamic Checkbox Is Selected

I am trying to make several fields in a HTML form validated, but only
when a dynamic checkbox is selected. I am not sure how to do this.

Here is a snippet of the dynamic checkbox code:
<%
Set RSLIST = Server.CreateObject("ADODB.Recordset")
SQLLIST = "SELECT * FROM Newsletters ORDER BY Newsletter_Name"
RSLIST.Open SQLLIST, Conn, 1, 3
%>
<%Do While Not RSLIST.EOF%>
<input type="checkbox" name="Newsletters"
value="<%=RSLIST("ID")%>"><%=RSLIST("Newsletter_Name")%>

I would like to make three fields (company, phone_work, license)
mandatory when one of the "ID" (i.e. ID 2) is checked.