Latest figures from the shopworkers' union USDAW revealed that 70% of staff had been verbally abused in the past 12 months, compared with just over 60% the previous year.
A massive 38% had also been threatened with violence, while 6% had been physically assaulted.
According to the survey, which came ahead of USDAW's Respect for Shopworkers week, almost half of all verbal abuse stemmed from a refusal to sell age-restricted products to those without identification.
Challenging shoplifters and refusing alcohol to intoxicated customers were also common triggers for verbal abuse, it said.
As C-Store went to press a female Costcutter employee from Evesham in Worcestershire was recovering from shock after a male customer vandalised the store she was working in and submitted her to a torrent of vicious verbal abuse. She had refused to serve him alcohol because she believed that he was buying it for an underaged girl.