Labor Day was made a federal holiday for employees of the U.S. government in 1894, originally scheduled as a day to celebrate labor and the trade union movement.

Labor Day throughout much of the world, where the day is often named International Workers’ Day, is held on May 1. In the United States and Canada, however, Labor Day is held on the first Monday of September — marking an unofficial end to summer.

A recent Gallup poll found approval of labor unions nearing a more than 50-year high at 64 percent, just below the 66 percent reached in the late 1960s and 1990s.

Today, picnics and barbecues are held on Labor Day to celebrate the remaining warm summer days. In a video posted to Twitter, Iowa Gov. Kim Reynolds recognized the recreational activities that take place each Labor Day, but said the holiday is about much more than the final picnic of the year.

Happy Labor Day! https://t.co/NFLeBo4pRl

— Gov. Kim Reynolds (@IAGovernor) 2 September 2019

“Labor Day really means so much more, it is the one day each year set aside to honor the achievements of the American worker, and to give those workers a day off as you’re celebrating with your family and friends in your union hall or city park,” Reynolds said. “I hope you’ll take time to reflect on the contributions the American worker makes to the strength and prosperity and [the] well-being of Iowa and our entire country.”

Presidential candidates, many of whom are campaigning in Iowa as caucus season heats up while the weather cools down, issued statements or gave remarks marking the holiday.

At a Labor Day picnic in Iowa City, former Vice President Joe Biden said unions built the middle class, adding there has been a war on labor for years — echoing statements he has made in the presidential debates.

Other candidates took to Twitter to show their support for unions and workers.

Sen. Bernie Sanders, I-Vt., tweeted, “[t]his campaign is about standing with working people everywhere against corporate greed. This Labor Day, join a #BernieSolidarity action near you!”

This campaign is about standing with working people everywhere against corporate greed. This Labor Day, join a #BernieSolidarity action near you! Find one at https://t.co/0gzurt3tS5

— Bernie Sanders (@BernieSanders) 2 September 2019

Sen. Elizabeth Warren, D-Mass., tweeted a similar message to Biden’s, saying “unions will rebuild the middle class.”

Unions built the middle class—and unions will rebuild the middle class. If we want more good American jobs, then we need stronger unions and more power in the hands of the people. I’m proud to be fighting alongside our unions. #LaborDay pic.twitter.com/uoAqIq9tH2

— Elizabeth Warren (@ewarren) 2 September 2019

Sen. Kamala Harris, D-Calif., rallied with union workers in Los Angeles to support their fight for fair labor practices, better wages and quality health care, according to a tweet.

This Labor Day, I joined union members at a rally in Los Angeles to fight for fair labor practices, better wages, and quality health care. Together we can ensure working people have the dignity that they deserve. pic.twitter.com/7nmAd0b6yS

— Kamala Harris (@KamalaHarris) September 2, 2019

South Bend Mayor Pete Buttigieg tweeted “[i]f we’re going to build a fair and prosperous future for us all, we urgently need every worker in America to have the opportunity to get ahead—and that means taking a bold new approach to strengthen unions for the next era. #UnionsForAll“

If we’re going to build a fair and prosperous future for us all, we urgently need every worker in America to have the opportunity to get ahead—and that means taking a bold new approach to strengthen unions for the next era. #UnionsForAll https://t.co/BgXYxmd3Kr

— Pete Buttigieg (@PeteButtigieg) 2 September 2019

The White House issued a statement calling American workers the “greatest labor force in the world.” President Donald Trump celebrated the holiday by going to one of his golf courses for the 227th day of the 955 he has been president.