More companies are starting or expanding wellness programs that aim to reduce their medical costs by improving their employees' health. They're asking workers to take physical exams, complete detailed health assessments and focus on controlling conditions such as diabetes. Along with that, many companies also are dangling the threat of higher monthly insurance premiums to prod workers into action. The Affordable Care Act is one reason the programs are spreading. The federal law calls for a 40 percent tax on expensive benefit plans starting in 2018, and many companies that offer employer-based coverage already have begun looking for ways to lower costs and avoid that tax.