Staff at Revenue and Customs (HMRC) have condemned "hare-brained" plans to remove items such as family pictures from work areas to boost productivity.
Revenue and Customs staff cannot have food at their desks
New rules in tax offices mean desks must be free from clutter to promote "efficient business processing".
The Public and Commercial Services union said the moves were "dehumanising" staff. The HMRC said the aim was to "provide improved service".
Non-essential items targeted include money, memorabilia and packed lunches.
Essential items that are allowed in workstations include calculators and pens.
The HMRC's Lean programme, which aims to improve efficiency, has already resulted in a work-to-rule and overtime ban among 14,000 civil servants.
Now an internal memo from a senior manager in North Wales has caused further controversy, with the document saying Lean has been successfully introduced into the main processing centres in North Wales.
It goes on to suggest that "its introduction is only the start of the Lean journey. Lean does not stand still. Much more needs to be done."
PCS union general secretary Mark Serwotka said: "By reducing staff to nothing more than machines on the whim of consultants, the department is undermining the morale of staff who face imminent job cuts and office closures.
"It is ridiculous that, unlike their colleagues working for the same organisation in the same office, this group of workers are being banned from having things such as a photo of a loved one on their desk."
The union said the HMRC's claims that Lean would deliver efficiency gains of 30% lay in "tatters".
The PCS also described the scheme as "hare-brained" and claimed there is a huge backlog of post from taxpayers.
An HMRC spokesman said: "Lean is all about offering a better service to our customers and staff. It is a key element in HMRC's plan to provide improved service and meet efficiency targets.
"Staff are asked to organise their desks when shared with colleagues to avoid clutter and to make sure they have everything set up to do their job effectively.
"Any suggestion that staff are restricted to a pen and cup on their desk is simply not true.
"Rather than making work boring and repetitive, staff are being invited to work with their managers to improve the way tasks and systems are developed."