An influential Iowa conservative will unveil a new pledge on Thursday for Republican presidential candidates, asking them to affirm socially conservative principles.

Bob Vander Plaats, the president and CEO of the group The Family Leader, is set to unveil a candidate pledge on Thursday morning in Iowa. Vander Plaats, the chairman of Mike Huckabee's 2008 campaign in Iowa, won't endorse a 2012 Republican candidate if they don't sign his pledge.