It says there has been a small increase in complaints over the past two weeks, mainly about cars on the Red and Blue Lines.
The CTA says winter months are more challenging because snow and ice get tracked into cars, and because more homeless people use the system.
It says cars are being cleaned daily by the same number of workers it has used in the past.
Amalgamated Transit Union Local 308 President Robert Kelly said in a statement Thursday: "Not only are they short about 50 servicers/cleaners, their paying overtime to servicers to work double shifts and giving motorman 1 day suspensions for not doing the job of the car servicer apprentices whose agreement came to an end on December 31, 2013 because of Forrest Claypool's refusal to talk with 308 union officials regarding this program."
