BOSTON — Courting unions on Labor Day, President Barack Obama denounced Republicans for a “constant attack on working Americans” and said he was using his executive power to force federal contractors to give paid sick leave to their employees.

Obama was met with resounding applause at a major union rally and breakfast in Boston on Monday when he said he had signed the executive order aboard Air Force One as he flew in to mark Labor Day. He said Republicans who claim the mantle of middle-class protectors are talking big, but they “have to walk the walk.”

Obama said opponents of his economic policies “won’t let facts or evidence get in their way.”

“You just wait, you look up at the sky and prosperity will come raining down on us from the top of whatever high-rise in New York City,” he said sarcastically. “But that’s not how the economy works.” He added that the GOP’s mindset has been “wrecking the economy for a long, long time.”

The Labor Day gesture to workers’ groups came as Obama works to smooth over tensions with the labor movement over his trade agenda. Major unions are opposing Obama’s push for sweeping new trade deals with Asia and Europe, with some threatening to work against Democrats who voted to support those talks in Congress. Unions have warned that the deals could lead to the widespread job elimination. Obama has signed a law providing money to retrain workers if their jobs get shipped overseas.

Under the executive order, employees working on federal contracts gain the right to a minimum of one hour of paid leave for every 30 hours they work. Stretched out over 12 months, that’s up to seven days per year. The order will allow employees to use the leave to care for sick relatives as well, and will affect contracts starting in 2017 – just as Obama leaves office.