(CNN) Republicans are seizing on the individual mandate’s penalty in the newly upheld health care law as proof President Obama broke his promise not to raise taxes on middle class Americans.

In the Supreme Court ruling on the law, Chief Justice John Roberts said the penalty on Americans who opt against buying health insurance is actually a tax, therefore making the individual mandate constitutional. Congress, Roberts reasoned, has the authority to assess taxes.

As it turns out the tax penalty in the president’s health care law was modeled after the reform plan passed in Massachusetts under then governor Mitt Romney.

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