New York Mayor Bill de Blasio (pictured in Manhattan on Monday) is shaping up for another showdown with Donald Trump

New York Mayor Bill de Blasio is shaping up for another showdown with Donald Trump.

De Blasio issued a mayor directive, which was sent around by senior NYPD figures on Tuesday, telling officers not to let ICE agents onto school ground unless they have a 'valid warrant', the New York Post reports.

The order states 'non-local law enforcement officers will not be permitted to proceed' beyond the reception desk at schools in New York City.

The mayoral memo was reportedly authorized by Chief of Department Carlos Gomez, and it demands a senior NYPD official must be contacted: 'if there is a disagreement between a principal and non-local law enforcement officer regarding access to the school or an officer insists/demands access'.

De Blasio issued a mayor directive telling officers not to let ICE agents onto school ground unless the have a 'valid warrant'. Donald Trump is pictured speaking on Tuesday

The move was apparently met with some push-back from NYPD brass, with one source telling the newspaper it was a 'ridiculous' plan.

'We work with law enforcement. That’s our job... we're supposed to work together,' the cop insider said.

The memo was sent just one day after Attorney General Jeff Sessions issued a 'dire threat' to sanctuary cities - such as New York.

Sessions warned the cities would no longer receive federal Department of Justice grants which are worth billions.

The mayoral memo was authorized by Chief of Department Carlos Gomez (pictured), and it demands a senior NYPD official must be contacted: 'if there is a disagreement between a principal and non-local law enforcement officer regarding access to the school

President Trump then reiterated his support for Sessions during a listening session with the Fraternal Order of Police on Tuesday, mentioning the Attorney General's 'big day' regarding his comments on sanctuary policies.

'That was a very important thing you did, and frankly, a very popular thing. It's great to have you with us,' Trump said.

Sessions knocked cities and various other jurisdictions for not communicating law-breakers' immigration status to the feds, sometimes releasing illegal immigrants from jail so they can do more damage.

Sessions warned the cities would no longer receive federal Department of Justice grants which are worth billions

'Such policies cannot continue,' Sessions implored on Monday.

'They make our nation less safe by putting dangerous criminals back on our streets.'

Sessions said he was 'urging states and local jurisdictions to comply with these federal laws.'

He said the Trump Justice Department will require compliance with immigration laws in order for the cities to receive grants through the Office of Justice Programs.