New plans to cut the amount of hours some cleaners work at Whipps Cross Hospital are "crazy" and could put patients at risk, it is claimed.
Union Unison says efforts to combat the spread of infection could be severely compromised if proposals to reduce the hours of 41 staff are approved.
The hospital's cleaning is contracted out to private firm Initial Facilities, a subsidiary of the Rentokil company.
It has proposed cutting 30 minutes from seven-and-a-half hour full-time working days and three-hour part-time evening shifts.
Initial employs around 300 staff at the Leytonstone hospital, including cleaners, porters and switchboard operators, and said the measures are "phase one" of a new efficiency drive.
Unison branch secretary Len Hockey said staff feared there were more cuts to come.
A one-month consultation has been launched with staff.
Mr Hockey said his union was considering industrial action.
He added: "Domestic staff play a vital role in keeping the hospital free from infection – these workers have barely sufficient time at the moment, with ‘good will’ often a factor in getting the job done.
"Cutting the hours spent cleaning the hospital is a crazy measure and may compromise standards of care."
Mr Hockey said he believed financial pressures on the hospital were to blame for the proposed cuts.
In comes in the wake of Whipps Cross Hospital being forced to close wards several times in recent years due to outbreaks of infections.
Most recently in February 2012 three wards and a care unit were shut due to an outbreak of the Norovirus.
The Guardian is awaiting a comment from Initial and Barts Health NHS, the trust which runs Whipps Cross Hospital.