New York's $9 congestion toll on drivers entering the most traffic-snarled parts of Manhattan appears likely to remain through the summer and possibly into the fall as a lawsuit challenging the Trump administration's authority to end the program moves forward.

U.S. Transportation Secretary Sean Duffy, who called the toll a "slap in the face to working class Americans and small business owners," had originally set a deadline of March 21 for the state to turn off the tolling program. When state officials refused, federal authorities set a new deadline of April 20. New York Gov. Kathy Hochul had said the state intended to ignore that deadline, too.

Now, though, the two sides in the legal fight have decided to slow things down. State and federal officials agreed to a briefing schedule for the lawsuit that allows for court filings through the end of July, and possibly into October, according to a letter Friday to the federal judge overseeing the lawsuit.

Federal officials also said they have no plans to seek an injunction that would stop the tolls while the lawsuit proceeds.

The Metropolitan Transportation Authority, the regional transit agency, filed the lawsuit challenging Duffy's decision to rescind the toll's federal approval in February. Congestion pricing advocates say it's meant to deter drivers and relieve traffic backups while providing billions of dollars in new revenue to the city's transit system.

The U.S. Department of Transportation did not immediately respond to an email seeking comment Tuesday. The U.S. attorney's office in Manhattan, which represents Duffy in the lawsuit, declined to comment.

The MTA also declined to comment, saying Friday's letter speaks for itself.

The fee started Jan. 5 on most drivers entering Manhattan neighborhoods south of Central Park. It comes on top of tolls drivers already pay to cross bridges and tunnels into Manhattan.

President Donald Trump, whose namesake Trump Tower and other properties are within the congestion zone, vowed to kill the plan as soon as he took office.