A proposed requirement that all Americans buy health insurance does in fact include a "tax" increase, according to the Senate -- even though President Obama insisted Sunday that it "absolutely" does not. 

Obama gave ABC News' George Stephanopoulos a stern talking-to Sunday for suggesting that the mandate to buy health insurance would amount to a tax. He even taunted the host for citing the dictionary definition of "tax" to make his point. 

"The fact that you looked up Merriam's Dictionary, the definition of tax increase, indicates to me that you're stretching a little bit right now," Obama said. 

But the language of the health care reform plan proposed by Sen. Max Baucus, D-Mont., explicitly labels the penalty attached to the mandate as an "excise tax." 

Penalties for failing to obtain coverage would range from $750 to $3,800 under the plan. This is addressed in a section labeled: "Excise Tax." 

"The excise tax would apply for any period for which the individual is not covered by a health insurance plan with the minimum required benefit," the Baucus plan says. 

Republican strategist Brad Blakeman said Obama just got busted. 

"The president cannot orate himself out of this one. If it feels like a tax, it says it's a tax -- Mr. President, it's a tax," Blakeman said. 

House Minority Whip Eric Cantor, R-Va., said Monday at a forum in Richmond that the House treats the penalty the same way. 

"The president was on TV last night or yesterday morning saying 'no no no, it's not new taxes,' whereas in this bill and in the Senate bill both, it calls what they are charging employers and individuals a tax. It's an IRS section of our bill," he said. 

The Baucus plan does not describe the requirement itself as a tax -- just the penalty. 

But Julian Epstein, former Democratic counsel to the House Judiciary Committee, said the requirement is no different from requirements to obtain auto insurance. 

"It's called personally responsibility," he said. 

Obama and Stephanopoulos got in a testy exchange over the matter Sunday on "This Week." 

"Under this mandate, the government is forcing people to spend money, fining you if you don't. How is that not a tax?" the host asked. 

Obama argued that the government would be providing tax credits for those who have trouble affording coverage, and that Americans who have insurance are already paying hundreds extra in premiums to cover uncompensated care. 

"That may be, but it's still a tax increase," Stephanopoulos said. 

"No. That's not true," Obama said. "I absolutely reject that notion."