ABC News/Matt Negrin

One of the groups that sued the government over the health care law and lost today is warning that young people are about to get whacked with a "big new tax."

One of the more popular provisions of President Obama's health law is a measure that lets young people stay on their parents' health insurance plans until they turn 26. Dan Danner, the president of the National Federation of Independent Business (the biggest group involved in the case), said after the court ruling he never disliked that particular rule - but he suggested that young people are in for a surprise when they grow out of it.

"This is a big new tax on you," Danner said of young people, on a conference call with the press. "The law is going to become less popular, not more."

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The tax Danner was talking about is the thrust of the Supreme Court's decision. With the help of George W. Bush appointee John Roberts, the court said the so-called mandate to buy health insurance is constitutional under Congress' power to tax people who don't buy it.

"When you turn 27, all of a sudden, you're going to have a potentially significant new tax," he said. (Actually, he probably meant to say 26, but that's beside the point.)

Danner issued the alerts: What if you're better off as a twentysomething paying $1,000 for a health plan with a high deductible, but the government forces you to buy a $6,000 policy "with all the bells and whistles included?" Also, what if the Obama administration determined that the tax is too low, and it wants to double it? Or even triple it?

"Could the money from this be used for a somewhat different purpose?" Danner wondered. "There are a lot of further questions going forward about this new tax."

Time will tell how that all plays out. In the meantime, Danner was asked if the massive court battle was worth it.

"Absolutely," he said. "It's been a long two-year effort, but certainly from where I am, we'd do it again in a heartbeat."

That pun was probably not intended.

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