The Royal Mail has ended Sunday postal collections after 17 years in what it calls an effort to improve efficiency.
Mail has been collected on Sundays for 17 years
It said mail had been collected from a sixth of its 118,000 post boxes and 50 business customers on Sundays.
Accounting for 1% of all mail posted, items collected on Sundays cost four times as much to process as those collected on other days, it said.
The Communication Workers Union (CWU) said the move would erode post services and cut staff's earning potential.
The move comes as thousands of postal workers are set to start voting on a new deal on pay and conditions after a series of strikes.
'Pursuit of profit'
Royal Mail reintroduced a Sunday collection in 1990.
The firm says it is now operating in a competitive postal market and stopping the Sunday collection was a way of reducing costs "with the minimum of disruption".
"Given the disproportionate cost of providing Sunday collections, and the low importance many consumers attach to such collections, ceasing this service makes commercial sense," it said.
The company has insisted it needs to modernise to survive as a business in the highly competitive mail industry.
But a CWU spokeman accused Royal Mail of "another reduction in the public service, caused by the race to the bottom with competition and the pursuit of profit".
"The union again calls on the government to undertake an urgent review of the impact of competition on postal services."