The little-known Medicare surtax may hammer millions in Obamacare tax battle

The Medicare surtax, a 0.9% tax on earned income above $250,000 for joint filers, may become a key issue in the midterm elections as Democrats look to fund Medicare. Millions of families are unaware they're paying this tax until tax filing time. The tax was introduced in 2013 as part of the Affordable Care Act.