In 2013, Shafer introduced a constitutional amendment capping the state income tax which passed the General Assembly and was approved by the voters in the 2014 general election. Shafer authored two controversial amendments significantly limiting taxation powers of local government in Fulton County. In 2005, Shafer attached an amendment to the charter of the City of Sandy Springs which prevented the mayor and council from increasing city property taxes above the existing millage rate without a referendum. Similar amendments were subsequently incorporated in the charters of the City of Milton and City of Johns Creek. More controversially, Shafer sponsored a legislative amendment prohibiting counties from collecting taxes in one area of a special services taxing district and spending those taxes in a noncontiguous area. The amendment affected only Fulton County. Senator Vincent Fort denounced the Shafer Amendment as "apartheid," saying it prevented Fulton County from taxing wealthy, predominately white homeowners in North Fulton and spending those taxes providing services to poorer areas of South Fulton. Shafer agreed that the amendment had that effect, saying that each area should pay for its own services, but called the reference to apartheid "erroneous and insulting." Fulton County unsuccessfully sued to overturn the Shafer Amendment, losing in front of both a Fulton Superior Court judge and the Georgia Supreme Court. Shafer supported Sonny Perdue for governor, endorsing him, contributing to his campaigns and making speeches on his behalf. He also served briefly as one of Perdue's floor leaders in the Senate. However, the two disagreed on budgetary issues. Shafer opposed Perdue's 2003 package of proposed excise and property tax increases, voting against even a scaled back version that only raised tobacco taxes. He also opposed Perdue's 2010 proposed tax on hospital bills, insisting that it be coupled with reductions in income and insurance premium taxes. Also, Shafer introduced zero-based budgeting legislation over Perdue's objections. When Shafer won passage of zero based budgeting in 2010 with Senate Bill 1, Perdue vetoed it. Shafer moved to override Perdue's veto during the 2011 legislative session. In late 2008, after Lieutenant Governor Casey Cagle announced that he would be running for governor in 2010, Shafer filed paperwork with the Georgia State Ethics Commission authorizing formation of a campaign committee to run for lieutenant governor. In early 2009, Shafer announced endorsements from a majority of the Republican members of the Georgia General Assembly and decisively defeated Senator Eric Johnson, who had also announced as a candidate for lieutenant governor, in straw polls held at county Republican conventions. On April 15, 2009, after Lieutenant Governor Casey Cagle announced that a debilitating spinal disease was forcing him to withdraw from the race for governor and instead seek re-election as lieutenant governor, Shafer released a statement wishing Cagle well and suspending his own campaign in order to "reevaluate political options."