Inspector General of police Joseph Boinnet has nullified President Uhuru Kenyatta's order that allowed matatus to be painted with graffiti.
The president had in 2014 lifted a ban imposed by the National Transport and Safety Authority (NTSA) on TV screens, music and graffiti on matatus.
According to NTSA, the ban was meant to promote safety on roads and keep windshields clear of graffiti.
President Kenyatta had argued that matatu graffiti was innovative and a source of livelihood for youths.
But on Wednesday, Inspector General of Police Joseph Boinnet said the president's moratorium was being used the wrong way.
"I celebrate our culture and I love art. But not one that celebrates gangsters or violence," he told Citizen TV anchor Jeff Koinange in an interview.
The police boss also admitted that his officers might have been relaxed in enforcing the ban
"Maybe we were a bit relaxed in the past but moving forward we have said enough is enough; if you are a PSV operator you better make sure that your vehicle is in the condition that the law prescribes. If you don't, don't say I didn't warn you," he said.
The recent crackdown on matatus over the so-called Michuki rules has forced matatu owners back to garages. The rules require matatus to have only one colour and a continuous yellow line painted on the sides, back and front.
"The 'Michuki Rules' were not suspended at all; we have always enforced them but at some point some of us relaxed," Mr Boinnet acknowledged.
Graffiti artists try to make each matatu look better than the next with custom designs covered in flashy colors, and state of the art entertainment.
The more glitzy and effervescent the matatu, the more prominent it becomes to attract passengers.