Bev Randles chairs The Missouri Club for Growth, which is part of a coalition urging lawmakers to override Gov. Jay Nixon's veto of the tax-cut legislation.
Randles said Friday her group won't support the re-election bid of anyone who votes against the veto override and likely would look for a challenger to set up a 2014 primary.
The head of the Missouri Chamber of Commerce and Industry also said the tax-cut legislation would be a high priority as it rates lawmakers.
The Legislature is to convene Sept. 11 to consider overriding bills vetoed by Nixon. Republicans hold supermajorities in both the House and Senate.