Retailers have warned that government plans to increase the age at which teenagers can buy knives and cigarettes is likely to lead to "conflict flashpoints" with shop workers.
The warning from the British Retail Consortium (BRC) comes as retail union Usdaw holds its annual respect for shop workers day.
According to the union, more than 10,000 physical assaults are made upon shop workers every year, with underage teenagers attempting to buy age-restricted products among the root causes of the harassment.
The awareness-raising day comes ahead of the raising of age restrictions on cigarettes and knives to 18 on October 1st.
The BRC insists it supports the changes, but claims the new regulations must be communicated to affected customers to avoid an increase in "threatening behaviour, verbal abuse and violence against shop workers".
"Checkouts are conflict flashpoints where restricted goods such as alcohol, cigarettes and knives are concerned. Saying 'no' can be unpleasant, particularly in the face of intimidation, verbal abuse and even violence," cautioned BRC director Kevin Hawkins.
Research conducted by the BRC itself shows that a quarter of small to medium-sized retailers expect to lose at least one member of staff through crime, violence or antisocial behaviour.
"That is unacceptable. No worker in any field of employment should be subjected to threatening or violent behaviour of any kind," Mr Hawkins added.
Announcing the raising of the age at which cigarettes could be bought at earlier this year, then public health minister Caroline Flint said: "Buying cigarettes has been too easy for under-16s and this is partly due to retailers selling tobacco to those under the legal age.
"The law change demonstrates our determination to stop this and to reduce the number of teenagers who smoke. This, in turn, will reduce the number of people with preventable diseases and the incidence of health inequalities."