Controversial plans to cut the hours of some cleaning staff at Whipps Cross Hospital are part of measures which will "improve productivity and efficiency", contractors have claimed.

Union Unison says efforts to combat the spread of infection could be severely compromised if the proposals are approved and has threatened industrial action.

Cleaning at the Leytonstone hospital is contracted out to private firm Initial Facilities, a subsidiary of the Rentokil company.

It wants to cut 30 minutes from seven-and-a-half hour full-time working days and three-hour part-time evening shifts, which would lead to a reduction in pay.

Unison says 41 staff will be affected but Initial says the figure is 36.

A spokesman for the firm defended the proposals in a statement today: "We have entered into a consultation period with 36 predominantly part time colleagues who may be affected by a slight reduction in working hours.

"This is part of an initiative designed to improve productivity and contribute to better patient care.

"The changes are the result of adopting more efficient working processes and investment in new equipment to eliminate waste, reduce delays and enhance cleaning standards delivered at the hospital."

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.

He told the Guardian yesterday: "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."

Barts Health NHS, the trust which runs Whipps Cross Hospital, has refused to comment.