Attorney General Jeff Sessions speaks at the U.S. Attorney's Office in Philadelphia, Friday, July 21, 2017. Associated Press/Matt Rourke Attorney General Jeff Sessions toughened his crackdown on so-called "sanctuary cities" on Tuesday, announcing that certain grant programs for cities and states would be conditional on whether local officials allow immigration agents access to local jails.

Starting in the fiscal year 2017, jurisdictions must allow immigration officers into detention facilities and provide 48-hours' notice before releasing an inmate who is wanted by immigration agents in order to be eligible for Byrne Justice Assistance Grants.

"So-called 'sanctuary' policies make all of us less safe because they intentionally undermine our laws and protect illegal aliens who have committed crimes," Sessions said in a statement.

"These policies also encourage illegal immigration and even human trafficking by perpetuating the lie that in certain cities, illegal aliens can live outside the law."

Sessions cited an incident that happened in San Antonio, Texas, on Sunday, in which 10 undocumented immigrants died after being transported in a sweltering tractor-trailer across Texas in an alleged human-smuggling case. Some Republicans have attributed the deaths to cities with "sanctuary" policies they say "entice" immigrants into crossing the border illegally.

Sessions' announcement on Tuesday marks a significant escalation in the Trump administration's approach to "sanctuary" jurisdictions, which implement a variety of policies that limit their police departments and jails' cooperation with federal immigration authorities. For instance, many cities opt not to honor federal requests to detain immigrants in jails unless the requests are accompanied by judge-signed warrants.

Previously, Sessions had only required that localities abide by the federal statute 8 USC 1373, which only requires that local officials not interfere with the exchange of information regarding people's citizenship or immigration status. But many "sanctuary cities" had argued that they already complied with that statute.

Sessions' critics have argued that his crusade against "sanctuary" policies will push undocumented communities further into the shadows, discouraging immigrants from reporting crimes committed against them out of fear they will be deported.

The move also comes as Sessions faces increasing public criticism from President Donald Trump over his recusal from the Russia investigation. Trump has now said multiple times he would not have nominated Sessions as attorney general had he known Sessions would recuse himself, prompting speculation over whether Sessions would resign.

Sessions, however, has said he will remain in the position “as long as that is appropriate.”