Janitors who clean Chicago Public Schools buildings said Thursday that schools are dirty because the private mega-company managing them has cut too much staff.

And if Aramark doesn’t agree to add 500 more custodians during contract negotiations, members of SEIU Local 1 will strike, union president Tom Balanoff told the Chicago Sun-Times in the wake of reporting that showed some 90 schools failing district-led “blitz” cleaning inspections.

Before the company took over custodial services in 2014, some 2,300 school janitors mopped and swept and polished the rooms where the city’s public schoolchildren learn and eat, but that number has been halved to about 1,100 currently, Balanoff and several janitors told the editorial board.

A strike vote has not yet been taken among the members of Local 1 that’s part of the coalition of labor unions with an ownership stake in the Chicago Sun-Times.

Bargaining on the new deal began Thursday. The current contract for the janitors expires on April 8, which would be the soonest they could walk off the job, though they plan to return to negotiations on April 13, a union spokeswoman said.

“We will obviously bargain with that and give them time to reach out to those who’d have to reach out about the issue of 500 janitors,” Balanoff said. “I think Aramark sold them a bill of goods, I think Aramark has to get its profit margin, and I think Aramark has been cutting corners left and right on equipment and people all along. But you know what, that’s Aramark’s problem. Quite frankly it’s CPS’s problem.”

CPS dispatched staff from its own facilities department and from Aramark to quietly conduct detailed “blitz” inspections on about a third of its schools whose janitors were managed by Aramark. Of the 125 schools they looked at, 91 failed, as the Sun-Times reported last month, with the worst of the findings in schools educating low-income students of color. The district did not examine the rest of the schools, whose cleaning as well as other facilities services, are overseen by Aramark and SodexoMagic.

Black aldermen have called for action, even Mayor Rahm Emanuel was “beyond outraged” at the results that CPS did not share with families or Local School Councils of any of the examined schools.

CPS has said that the problems occurred in schools where services were handled by various entities, and that consolidating all facilities responsibilities under Aramark or SodexoMagic management should resolve many of the issues. That $427 million rollout was supposed to happen last July 1 but has been postponed a year. The district refuses to release the contracts, the last of which was signed in January.

CPS, SodexoMagic and Aramark did not respond to requests seeking comment.

SodexoMagic oversees an additional 600 janitors in schools they manage, and CPS directly employs another 825.

Janitors who accompanied Balanoff described how they lack for supplies when cleaning their schools that used to have more people on the job.

Maxine Gladney, a 16-year-veteran currently at Powell Elementary School, said her school’s four janitors were cut to three. She’s expected to clean 14 to 16 classrooms during her 8-hour shift, plus six bathrooms, a staircase and the school’s library, using a cleaning solution that’s mostly water.

“We ask for supplies, they tell us it’s not in our budget, Aramark tells us,” Gladney said. “I mean I have seven grandchildren in CPS. I want my school to be sanitized like I would like my grandchildren’s school, my home, I keep my home sanitized.”

The machines Aramark brought in to clean floors more efficiently break or can’t easily be moved from floor to floor, said Judith Jenkins, who works four-hour shifts at Ashburn Community Elementary School. Even when they are functioning, she said, “There’s corners and curves and grooves, I still have to go in behind and what, mop” using blue microfiber pads.

Sometimes the women bring in supplies from home to augment — “and we shouldn’t have to,” Jenkins said.

Maria Villegas’ school, Sayre Language Academy, also lost a staffer.

“At every school we need more manpower,“ she said through an interpreter. “Most of us stay 20 or 30 minutes after our shift is done to get our work done.”