Office staff in the Northern Health Trust have been told they are now responsible for vacuuming, dusting and keeping their own work area clean.
A memo seen by BBC News NI said domestic staff would continue to clean areas including kitchens and toilets.
The trust said there had been a review of cleaning services and was "mindful of the need to protect the health of everyone who uses our premises".
The Unite union said the idea was "absurd".
It means that health professionals including social workers, occupational health therapists and district nurses, as well as fulfilling their normal duties, are required to mop floors and remember to place their bins outside their office door to be emptied.
While all cleaning materials will be supplied, staff are reminded to use a step stool that is provided when cleaning shelves above head height.Image caption Kevin McAdam from Unite said the move would distract people from their work
Kevin McAdam, Unite's regional officer, said this was a "blatant waste of public funds in an effort to manage a directorate budget within the trust" and called on the trust to reverse the decision.
"There is nothing wrong with trying to save money or indeed use money wisely, but this is penny wise pound foolish," he continued.
"So you are asking people on senior salaries to do other roles and this is not in any way demeaning cleaners - they are a vital part of the team in the health service."
The Northern Health Trust is the only health trust expecting staff to clean their work area.
Mr McAdam said everyone had their own specific role to play.
'Waste of money'
"This is simply the greatest waste of money at this time," he said.
"Cleaners do a valued role in the health service and are a valued part of the health team, but distracting senior clinicians from their equally valuable role just makes a mockery of the service.
"Do we pay our taxes to train nurses allied health professionals and other senior office based staff to clean their rooms or provide direct clinical care to patients?"
Another health union, NIPSA, has advised its members in the Northern Health Trust that carrying out duties such as mopping and dusting went far beyond what can be expected by the trust.
"NIPSA would remind staff they should not undertake duties in which they have not been trained, and where no risk assessments have been documented by management," said a NIPSA statement.
The union said it would hold meetings with members in Antrim, Ballymena and Coleraine over the coming weeks.
Basic equipment available
A spokesperson for the Northern Health Trust said: "To ensure we can meet the highest standards for environmental cleanliness in areas where patients and clients are cared for, we previously reprioritised cleaning in administrative areas.
"We focus on cleaning staff washrooms, kitchens and public areas including meeting rooms.
"We have, however, asked staff to keep their office spaces clean and tidy and have made available some basic equipment such as vacuum cleaners."
The memo said domestic services staff would continue to clean the corridors and staircases, staff kitchens and toilets, meeting rooms and empty office bins that are left in the corridor.
Mr McAdam said asking office staff to mop and vacuum was not a good use of staff or resources.
"While Unite understands the trust will retain cleaners in clinical areas it simply ignores the large number of community nurses, health visitors, school nurses, pathology staff and many others who provide a clinical service from an office based environment.
"It is absurd that they should give that valuable time to replace other workers in a bid to save money."
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