A survey carried out by the union found verbal abuse of shopworkers rose by 35 per cent last year, with as many as half a million suffering it on a daily basis.
One shopworker said: 'Some customers seem to assume that, because someone works behind a counter, they are stupid and a target for rudeness and arrogance.'
Another said: 'I have worked in retail for eight years and, during that time, I've been sworn at and talked down to by customers - even when I was eight months pregnant.'
Usdaw is launching a campaign to highlight the problem this Wednesday. On national Respect for Shopworkers Day, union members will hand red cards to shoppers bearing the words: 'Usdaw united against abuse against shopworkers'.
Usdaw general secretary John Hannett (pictured above) said: 'Our simple message is that retail workers are not verbal punchbags for shoppers to take out their frustrations on. They are human beings and have the right to work in a non-threatening environment.'
The increasing number of physical attacks on retail staff is also a concern for the union. Last year, 20,000 retail workers were assaulted.
Hannet added: 'Every day, our members suffer a terrifying catalogue of physical abuse - being stabbed, hit with iron bars and threatened with dirty syringes.'