Freedom from Fear is run by the Union of Shop, Distributive and Allied Workers (Usdaw) and seeks to prevent violence, threats and abuse of shopworkers.
The news comes at the launch of Respect for Shopworkers Week which runs from Monday (November 14) until Sunday (November 20).
'I was shocked'
Shadow Chancellor Mr McDonnell said: “I was personally shocked to hear about the abuse that shopworkers can receive on what can be a daily basis. No one should have to go to work expecting abuse.
“Too often employees are confronted with violence, threats and abuse while serving the public.
“It is really important we stand together and ask people to keep their cool and respect shopworkers, especially as we approach the busy Christmas shopping period.
He added: “I will continue to work with Usdaw to provide shopworkers the support they need and deserve.”
According to Usdaw, one in 10 shopworkers have been assaulted while nearly one-third do not report the incidents.
Interim results from a Freedom from Fear survey also suggests that almost half of shopworkers are verbally abused.
'We are grateful to John McDonnell'
Full results from the research are due to be published by Usdaw in 2017.
The union's general secretary, John Hannett, said: “We are grateful to John McDonnell for supporting our campaign to keep our members safe at work.
“Often, in the court of their duties, shopworkers are expected to deal with tense and difficult situations.
“Unfortunately, these can escalate to verbal abuse and assault.”
Mr Hannett said over 300 shopworkers are assaulted every day.
He added: “It is time to say 'enough is enough'.
“Parliament has placed the legal obligation on shopworkers to enforce the law in relation to age restricted sales. Parliament must also ensure that the law also protects shopworkers who are doing their job.
“Politicians and members of the public must work together to ensure that shopworkers get the respect they deserve.”
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