<p>A popular middle class tax benefit could become one of the first casualties of the Affordable Care Act’s so-called Cadillac tax, affecting millions of voters.</p><p>Flexible spending accounts, which allow people to save their own money tax free for everything from doctor’s co-pays to eyeglasses, may vanish in coming years as companies scramble to avoid the law’s 40 percent levy on pricey health care benefits.</p><p>“They’ll be one of the first things to go,” said Rich Stover, a health care actuary and principal at Buck Consultants, an employee benefits consulting firm.