The growing use of tagging devices in workplaces to transmit information to staff - but also to track their work - has been condemned by the GMB union. Some 10,000 UK workers, mostly in retail distribution warehouses, had been affected but many had refused to co-operate and resigned, the GMB said.
It said the tags, which can monitor breaks and toilet trips, were turning workplaces into "battery farms".
A south Wales firm that had introduced the devices said "everyone likes" them.
The tags, containing computers linked to local radio networks and satellite tracking technology, can speed up orders by allowing information to be transmitted directly to workers.
"The idea is to track work all the time and, although it brings efficiencies, it does not take into account human needs," said GMB national officer Paul Campbell.
"We are receiving daily reports of people just walking away from the job," he said.
The union claimed staff turnover had reached 300% in some affected workplaces.
General Secretary Paul Kenny said: "The use of this technology needs to be redesigned to be an aid to the worker rather than making the worker its slave." 'Efficiency improvements'
The Peacock Retail Group, in Nantgarw, south Wales, said its introduction of 28 wearable and six truck-mounted terminals, and a wireless local area network, had "dramatically" improved distribution of goods.
"Everyone likes the wearables because they are comfortable to wear and easy to use," the firm said.
"The result is that the team finds it easier to do the job. This in turn leads directly to efficiency improvements."
Supermarket giant Tesco said its technology could not track staff, but helped them correctly select products and get them to stores more quickly.
"Our staff tell us that this has made their job easier, creating less paper and helping them to pick [goods] more accurately," said a Tesco spokesman.
Author of a report on the tags for GMB, Durham University's Professor Michael Blakemore, warned that because the tags had to be held at a certain angle to function they could lead to new industrial injuries. BBC News