Several 2012 Republican presidential candidates are slated to participate in an Iowa bus tour that seeks to make returning the country’s monetary system to the gold standard a key election issue.

The Iowa Tea Party and the group American Principles in Action announced that they are launching their 18-day bus tour starting June 13.

Republicans Michele Bachmann, Herman Cain, Newt Gingrich, Gary Johnson, Tim Pawlenty and Rick Santorum are scheduled to speak during at least one stop on the tour, according to Andy Blom, executive director of American Principles in Action. All are either running or contemplating a run for president in 2012.