CHICAGO (AP) -- From worker rights rallies to marches for social justice, activists around the globe will kick off May Day demonstrations on Thursday.

In some countries, it's a public holiday honoring labor, but activists planning marches in the United States say much of their message is about fighting back against President Donald Trump's policies targeting immigrants, federal workers and diversity programs.

Thousands are expected at demonstrations from Tokyo to Chicago. In some parts of the U.S., though, fear sowed by the Trump administration is expected to keep some immigrants home.

"Everybody is under attack right now," said Jorge Mujica, a longtime labor leader from Chicago, where May Day rallies historically have had a large turnout.

The roots of May Day, or International Workers Day, stretch back over a century to a turbulent and pivotal time in U.S. labor history.

In the 1880s, unions pushing for better workplace conditions began advocating for an eight-hour workday with widespread demonstrations and strikes. In May 1886, a Chicago labor rally turned deadly when a bomb was thrown and police retaliated with gunfire. Several labor activists, most of them immigrants, were convicted of conspiracy to incite violence among other charges. Four were hanged.

Unions later recommended that the workers be honored every May 1. A sculpture in Chicago's Haymarket Square commemorates them with an inscription that reads: "Dedicated to all workers of the world."

May Day marches, rallies and riots have taken place worldwide in recent years as unions push for better rights for workers, groups air economic grievances or activists call for an end to the war in Gaza.

While most demonstrations have been peaceful, there have been clashes with police.

Last year, police in Paris fired tear gas as thousands of protesters marched through the French capital, seeking better pay and working conditions. In New York City, May Day demonstrations coincided with rising tensions at college campuses over pro-Palestinian student encampments, resulting in numerous arrests.

This year, organizers in numerous cities, including New York, are calling for unity across many causes and groups.

"We're organizing for a world where every family has housing, health care, fair wages, union protection, and safety -- regardless of race, immigration status, or zip code," the American Civil Liberty Union of New York said in a statement.

Other notable U.S. demonstrations include a workers rally at Philadelphia City Hall with Vermont Sen. Bernie Sanders and demonstrations at the Colorado State Capitol and in Los Angeles, Seattle and Washington, D.C.

While labor and immigrant rights are historically intertwined, the focus of May Day rallies in the U.S. shifted to immigration in 2006. That's when roughly 1 million people, including nearly half a million in Chicago alone, took to the streets to protest federal legislation that would've made living in the U.S. without legal permission a felony.

Crowds for May 1 demonstrations have since dwindled with advocacy groups splintering and shifting activism arenas such as voters rights.

This year in Chicago, organizers say activism starting Thursday will last until Cinco de Mayo with boycotts and walkouts. Their focus is workers' rights but also rising anti-immigrant rhetoric from Trump's administration.

Organizers acknowledge a chilling effect on immigrant communities since Trump has cracked down on enforcement, especially in so-called sanctuary cities including Chicago. They're expecting lower numbers of immigrants but are expanding their outreach to more unions, including for teachers and nurses.

"There's a lot fear out there," said Omar Lopez, a longtime Chicago organizer.

In some countries, May Day is a public holiday for workers, including France, Kenya, Russia and China, where it lasts five days.

It's also a traditional spring celebration that's observed in ways that don't involve marching in the streets or civil disobedience.

In Hawaii, May 1 is called Lei Day, which isn't an official holiday, but a statewide celebration of the Hawaiian culture and the aloha spirit through the creation and giving of lei -- usually a necklace of flowers.

Elsewhere, people mark the holiday by leaving May Day baskets filled with gifts and flowers on the doorsteps of friends. The city of Annapolis, Maryland, is set to hold its 70th May Day Basket Competition, where residents and businesses outdo each other for the best floral arrangements.

"It's our community's way of saying goodbye to winter and welcoming the beauty and energy of spring," Annapolis Mayor Gavin Buckley said.