PHILADELPHIA (WPVI) -- A massive crowd gathered in Center City Philadelphia on Thursday for International Workers' Day, or May Day.
Across the United States, organizers framed this year's protests as a pushback against what they see as the Trump administration's sweeping assault on labor protections, diversity initiatives and federal employees.
In Philadelphia, labor and immigration leaders joined Vermont Senator Bernie Sanders outside City Hall for the "For the Workers, Not the Billionaires May Day Rally."
"Today we have a government of the billionaire class by the billionaire class and for the billionaire class, and we will not allow that to continue," he said.
Chopper 6 was overhead as demonstrators marched around Center City. Just after 7 p.m., a smaller crowd of people could be seen shutting down the intersection of Broad and Vine streets as police moved in to make arrests.
Philadelphia police say 70 people were arrested for obstruction of the highway.
"While the demonstration was intended to be peaceful, it led to the blockage of a major roadway, causing significant traffic disruptions and creating safety concerns for both protestors and motorists. Officers on the scene issued multiple warnings instructing participants to clear the highway," police said in a statement.
Labor leaders say they're standing against Trump's policies targeting workers, immigration and diversity programs.
"We are committed to standing with our union brothers and sisters, our working-class allies, immigrant rights groups, and community allies to fight for a future where all of us, not just the wealthy elite, can live and thrive in," said Philadelphia AFL-CIO President Daniel P. Bauder.
Trump argues he's delivering on his campaign promises surrounding immigration and the economy.
Union members say they're using their power to fight for their rights, vital services, wages and more. That includes AFGE LOCAL 1793, which represents employees at the Philadelphia VA Medical Center.
"All of this is greatly impacting us and creating a lot of stress and chaos at our medical center, so we're here to not only express the issues we're having when the veterans affairs to support our brothers and sisters in solidarity," said Yule Owens Jr., AFGE Local 1793 executive vice president.
Trump also argues he's making the government work for the taxpayers again through his executive orders and new initiatives, including downsizing the federal government.
The roots of May 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.
The Associated Press and ABC News contributed to this report.