According to the Supreme Court, the fines for not having health insurance is a tax. Forget that it was never called a tax when it was being considered in Congress in 2009. Forget that taxes must originate in the House, not the Senate, which is where Obamacare originated. If the Supreme Court says it is a tax, then it is a tax.
By similar logic, then, the fine that Obama wants to charge states which do not set up exchanges is also a tax, not a fine. However, this tax was declared not by Congress, but by the Department of Health and Human Services. The executive branch cannot create a tax.
States should, and MUST challenge this unconstitutional tax.