In his 4/27/2012 Forbes blog post, Avik Roy explains, "How Obamacare Will Make Health Savings Accounts More Costly".
It hinges on how the Obama administration defines "actuarial value".
Given the nature of HSA's (which are designed to allow consumers to pay larger amounts than in conventional insurance premiums in exchange for greater control over how that money is spent), this will make HSA's "actuarial value" look artificially low via these government yardsticks.
Read the whole piece for more details, including why this moves us in the wrong direction away from free-market reforms.