From barbecues to getaways to shopping the sales, many people across the U.S. mark Labor Day — the federal holiday celebrating the American worker — by finding ways to relax.This year is the 130th anniversary of the holiday, which is celebrated on the first Monday of September. While actions by unions in recent years to advocate for workers are a reminder of the holiday’s activist roots, the three-day weekend it creates has become a touchstone in the lives of Americans marking the unofficial end of summer.Here’s what to know about Labor Day:How did Labor Day become a federal holiday?Its origins date back to the late 19th century, when activists first sought to establish a day to pay tribute to workers.The first Labor Day celebration in the U.S. took place in New York City on Sept. 5, 1882, when some 10,000 workers marched in a parade organized by the Central Labor …