Royal Mail has been accused of keeping tabs on posties - including flagging when they are stood still.
A Commons hearing was told about digital devices that workers carry that can monitor their movements.
It came during a fiery meeting of the Commons Business, Energy and Industrial Strategy Committee.
Royal Mail is under pressure to resolve a dispute with 115,000 postal workers in a bitter row over pay, conditions and job security.
The hearing was shown a map, with yellow dots pinpointing when workers are not moving.
The bigger the dot, the longer the person was stood still, the hearing was told.
Darren Jones, chair of the committee, said: “I think it is clear from the evidence that you are using technology to encourage people to be more quick, and ranks them against their colleagues about who is and isn’t quicker at delivering their letters.”
Royal Mail boss Simon Thompson said the use of the technology in question, known as Outdoor Actuals, had been agreed with the Communication Workers Union.
He told the hearing: “It is not information that is available in real time, we don’t track the postal workers in real time, nor do we nudge them to ensure they go at the right pace.”
Mr Thompson was hauled back to give evidence after the committee judged what he said during a previous session was not “wholly accurate.”
He was quizzed on whether Royal Mail urged workers to prioritise parcels over letters.
Mr Thompson insisted: “Our policy is absolutely clear that letters and parcels have exactly the same priority.”
Yet the committee was shown various posters from delivery offices suggesting the opposite.
Mr Thompson, giving evidence under oath, claimed these were related to days on and around strike action only.
Mr Jones hit, revealing it had been sent video and audio evidence suggesting Royal Mail managers had told workers over many months to “just do as I tell you” and deliver tracked items and parcels first.
He quoted a postal worker from Cambridgeshire who said that for at least 18 months “we have been told on a daily basis through huddles on the shop floor from our line manager that we are to prioritise parcels over letters.”
Mr Thompson insisted: “It is not our policy but in the realities of industrial action we have to apply a different policy.”
Mr Jones put it to him: “You are recognising that what you told the committee last time was inaccurate?”.
Mr Thompson claimed it was about “context”.
But Mr Jones said: “Are there really that many rogue managers and postal workers dispersed through the entire Royal Mail network going against company policy, or is all this just a sham?”