The Trump administration has moved to reopen the cases of hundreds of undocumented people who were reprieved from deportation under Barack Obama, according to government data, court documents and interviews with immigration lawyers.

Donald Trump signaled in January that he planned to dramatically widen the net of undocumented immigrants targeted for deportation, but his administration has not publicized efforts to reopen immigration cases. News of the administration’s effort represents one of the first concrete examples of the crackdown and is likely to stir fears among tens of thousands of undocumented people who thought they were safe from deportation.

Cases were reopened during the Obama administration, but generally only if a person had committed a serious crime, attorneys said. The Trump administration has sharply increased the number of cases it is asking the courts to reopen, and its targets appear to include at least some people who have not committed any crimes since their cases were closed.

Between 1 March and 31 May, prosecutors moved to reopen 1,329 cases, according to an analysis of data from the Executive Office of Immigration Review (EOIR). The Obama administration filed 430 similar motions in the same period in 2016.

Jennifer Elzea, a spokeswoman for US Immigration and Customs Enforcement (Ice), confirmed the agency was now filing motions to reopen cases where illegal immigrants had “since been arrested for or convicted of a crime”.

It is not possible to tell from the EOIR data how many of the cases the Trump administration is seeking to reopen involve immigrants who committed crimes after their cases were closed. Attorneys said some of the cases were being reopened because immigrants had been arrested for serious crimes, but said they were also seeing cases involving people who had not committed crimes or who were cited for minor violations such as traffic tickets.

“This is a sea change,” said the attorney David Leopold, former president of the American Immigration Lawyers Association. “Before, if someone did something after the case was closed out that showed that person was a threat, then it would be reopened. Now they are opening cases just because they want to deport people.”

Elzea said the agency reviewed cases “to see if the basis for prosecutorial discretion is still appropriate”.

In 2011, Obama initiated a policy change, pulling back from deporting migrants who had formed deep ties in the US and whom the government considered no threat to public safety. Instead, the administration would prioritize undocumented migrants who had committed serious crimes.

Between January 2012 and Trump’s inauguration on 20 January 2017, the government shelved about 81,000 cases, according to Reuters analysis. These so-called “administrative closures” did not extend full legal status to those whose cases were closed, but they did remove the threat of deportation.

Trump signed an executive order overturning the Obama-era policy on 25 January. While criminals remain the highest priority for deportation, anyone in the country illegally is now a potential target. In cases reviewed by Reuters, the administration explicitly cited Trump’s executive order in 30 motions as a reason to put the immigrant back on the court docket.

Since immigration cases are not generally public, Reuters was able to review only cases made available by attorneys. Motions to reopen closed cases have been filed in 32 states, with the highest numbers in California, Florida and Virginia, according to the review of EOIR data. The bulk of the examples reviewed were two dozen motions sent over the span of a couple of days by the New Orleans Ice office.

Sally Joyner, an immigration attorney in Memphis, Tennessee, said one of her Central American clients, who crossed the border with her children in 2013, was allowed to stay in the US after the government filed a motion to close her case in December 2015. Since crossing the border, the woman has not been arrested or had trouble with law enforcement, said Joyner, who asked that her client’s name not be used because of the pending legal action.

Nevertheless, on 29 March, Ice filed a two-page motion to reopen the case against the woman and her children. When Joyner queried Ice, an official said the agency had been notified that her client had a criminal history in El Salvador, according to documents seen by Reuters.

The woman had been arrested for selling pumpkin seeds as an unauthorized street vendor. Government documents show US authorities knew about the arrest before her case was closed.

Dana Marks, president of the National Association of Immigration Judges, said revisiting previously closed matters would add to a record backlog of 580,000 pending immigration cases.

“If we have to go back and review all of those decisions that were already made, it clearly generates more work,” she said. “It’s a judicial do-over.”