Undocumented immigrants are being swept off the streets by masked officers in plainclothes who refuse to give their names. Parents are being handcuffed in front of young children and escorted together onto buses and into detention centers. Officers are tackling people and smashing car windows as they make arrests.

Videos of arrests like these have gone viral on social media and sparked protests and outrage as the United States reckons with the ramifications of the Trump administration’s push to deport millions of unauthorized immigrants.

So what is and isn’t illegal when ICE makes an arrest?

U.S. Immigration and Customs Enforcement was created after the Sept. 11, 2001, terrorist attacks as part of a major overhaul of the federal national security apparatus. Congress gave the agency substantial authority over how immigrants who do not have a legal status in the United States are detained and deported. And while the Trump administration has upended norms, much of what the public is seeing is permitted under U.S. law.

If President Donald Trump’s massive spending bill is approved, undocumented immigrant arrests and deportations are expected to dramatically ramp up. Here’s what to know about how officers conduct an arrest.

What to know

Immigration during Trump’s second term

Trump’s aggressive crackdown: Since returning to the White House, President Donald Trump has made immigration enforcement one of his top priorities. He issued a series of executive orders that include declaring a national emergency at the U.S.-Mexico border, deploying hundreds of troops there and attempting to end birthright citizenship for the children of noncitizens, a move that a federal judge has temporarily blocked. The administration has also largely closed access to the asylum process, suspended refugee resettlement and ended temporary humanitarian protections for about 350,000 Venezuelans who sought refuge in the United States. These policies have created widespread panic and confusion in immigrant communities across the country.

More resources diverted: Trump has promised to deport millions of immigrants who are in the country illegally, and administration officials have directed U.S. Immigration and Customs Enforcement officials to aggressively ramp up the number of people they arrest, from a few hundred per day to at least 1,200 to 1,500. To meet these goals, the administration has enlisted personnel from the FBI, U.S. Marshals, the Drug Enforcement Administration, the Bureau of Alcohol, Tobacco, Firearms and Explosives, and the Federal Bureau of Prisons. To quickly increase ICE’s detention capacity, the administration has begun to send migrants to the Guantánamo Bay Naval Base in Cuba.

Pushback in the courts: Advocacy groups and others have filed lawsuits over many of Trump’s new policies. Officials in 22 states, plus D.C. and San Francisco, have sued over Trump’s birthright citizenship executive order. Lawyers for the American Civil Liberties Union, the National Immigrant Justice Center and others have challenged the Trump administration’s claim that there is an “invasion” on the border to justify summarily expelling migrants without giving them a chance to apply for asylum.