$(document).ready(function(){
  $('input#non_reg_user_newsletter').click(function(){
    var first_name = $('input[name=first_name]').val();
    var last_name = $('input[name=last_name]').val();
    var email = $('input[name=email]').val();
    var business = $('input[name=business]').val();

    if(!first_name || !last_name || !email || !business){
      alert('Please fill out the form entirely - all fields are required.');
      return false;
    }

    return true;
  })
})