Employers are increasingly considering shifting retirees out of their health plans and into Medicare because of the Patient Protection and Affordable Care Act. But plenty of hurdles stand in the way.

Aon Hewitt's latest retiree health care survey revealed, perhaps unsurprisingly, that more than 60 percent of employers are reassessing their long-term retiree health strategies because of the PPACA.

Aon said it found that more than a quarter of companies would consider a retiree health care "settlement strategy" for all or a portion of their retiree group, "if the market environment could support it on a cost-effective basis."