Democratic presidential front-runner Hillary Rodham Clinton attacked Pfizer Inc.'s plan to move its tax address to Ireland through a merger with Allergan PLC, saying it would hurt U.S. taxpayers and urging a crackdown on such deals.

"This proposed merger, and so-called inversions by other companies, will leave U.S. taxpayers holding the bag," she said in a statement released Monday by her campaign. "As president, I will fight to reform our tax system to reward growth, innovation and job creation here in the United States. We cannot delay in cracking down on inversions that erode our tax base."

She vowed to release a proposal in the coming weeks to curb similar transactions. Her two main Democratic competitors, Sen. Bernie Sanders and former Maryland Gov. Martin O'Malley, and lawmakers from their party also denounced the merger as an example of how the system favors corporations more than middle-income individuals. Republican front-runner Donald Trump also criticized the merger.