WASHINGTON (AP) — Requirements that medium-sized and large employers offer insurance coverage or face fines are one of the most complicated parts of President Barack Obama's health care law. While most of the estimated 160 million Americans with job-based coverage will not see not see major changes when the law takes full effect next year, the so-called employer mandate will be important to millions of workers, particularly in low-wage industries. The Affordable Care Act, as the law is known, actually has two mandates on employers, part of ''shared responsibility'' provisions to ensure that companies keep offering coverage. Think of them as the big stick and the smaller stick.