Employees on zero hours schemes are too afraid to search for a new job and feel excluded from the sense of security other full-time workers enjoy, a study has shown.
Conciliation service Acas said it was receiving around 70 calls a week about zero hours contacts, and a feeling of "effective exclusivity" of being tied to a single employer was emerging as a major concern.
Their data showed many zero hours workers experienced "a deep sense of unfairness and mistrust".
The Government has been consulting on the use of zero hours contracts amid calls from unions and campaign groups to have them banned.
Labour has pledged to tackle abuses of zero hours contracts if it wins the next general election.
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