CHICAGO (AP) — Immigrants and their allies are preparing for May 1 rallies nationwide and say there's renewed momentum to fight back against President Donald Trump's policies and more collaboration among different advocacy groups.

Around the world, union members have traditionally marched on May 1 for workers' rights. In the United States, the event became a rallying point for immigrants in 2006 when more than 1 million people marched against a proposed immigration enforcement bill.

Since then, the U.S. marches have waned in size, but activists expect participation to surge this year because immigrant groups are working with organizations such as the Women's March. Also, many businesses with immigrant ties are closing or allowing employees to participate without penalty.

Activists in major cities including Chicago and Los Angeles expect tens of thousands of people to participate in Monday demonstrations, along with demonstrations in smaller cities.