They predict the move could cause a spike in crime.
Mayor Tony Mack has suspended operations at the Vice and Tactical Anti-Crime units and ordered those officers out walking a beat.
Mack, who laid off 105 cops two weeks ago because of budget problems, is now cutting back on overtime and telling the police department to redeploy about two dozen personnel to foot patrol.
"We've heard the people, and the people want to see their police officers. They want to see them on the street. They want to see them where they know crime takes place," said Mayor Mack.
Police unions call the move mind-boggling. They say cutting the units that deal with the most aggressive criminals and violent offenders - and having those 23 detectives walk the streets - makes no sense.
"It's nice for community policing, but if we're going after criminals you need SWAT teams, you need the TAC units. You need to go after them. You're not going to catch a criminal walking on foot," said Sgt. Mark Kieffer of the Superior Officers Association.
"We've got gangs, we've got guys with weapons. Now you're going to have nobody to investigate that," said Jim Carlucci of Crimestoppers of Trenton.
Some residents support putting at least some of the officers on foot patrol.
"When you're out here you get to know the citizens, you get to know the people around and you know what's going on," said Tracey Chescon.
Over the last several years anti-crtime and vice units have made more than a thousand arrests, seized hundreds of weapons and confiscated drugs with a street value of over $5 million.
Phone store manager Hector Davila was shot in the leg last month in a struggle with two masked gunmen who tried to rob his shop. He worries about what will happen to crime without the specialized units.
"Lots of drug activity, prostitution, whatever you want to call it. They're going to be out rampant, crazy," Davila said.
Mayor Mack says if things don't go well he would consider tweaking his plan, but for now the vice and anti-crime officers will be walking a beat.
