This is the problem faced by all in every industry.
This problem may be overcome by ,as you said - Providing Tea.
Ask the employees if they have any difficulties, if it is genuine, try to cover it.
Not reminding this isssue, try to include performance oriented pay to all shifts, in particualr it may work for these peoples. (don't say that you introduce this to cut the sleep).
Instruct the supervisors to be friendly (to make the environment lively, interaction with the workers - even they can crack jokes). Let they have frequent rounds around the work area.
28th April 2009 From India , Bangalore
4th August 2013 From United Kingdom, Ware
Providing tea in night shift is different. sleeping while on duty, blaming supervisor and absenteeism supreme court has look very serious.
S G ARAVIND
28th September 2013 From India, Bangalore
8th February 2014 From United Kingdom, Ware