Controversial zero-hours work contracts are being used by firms to strip staff of employment benefits and rights, a group of MPs has warned.
Some companies were deliberately "dodging" their responsibilities, the Commons Scottish Affairs Committee said, and other businesses were suffering because they were being undercut by unscrupulous employers.
The comments followed a meeting MPs held with Scottish officials from USDAW, the Union of Shop, Distributive and Allied Workers, in Falkirk. The committee said it had heard evidence firms were using "zero-hours" contracts when there was no justifiable business need.
Figures suggest up to one million people across the UK, including tens of thousands in Scotland, are thought to be on zero-hours contracts.
The Coalition Government has pledged to crack down on employers who misuse the contracts. But ministers insist they can be used legitimately and say they have no plans for a ban.
Unions say they exploit workers by expecting them to be at employers' beck and call and offering little or no chance to save or plan ahead.
Ian Davidson, the Labour MP who chairs the committee, said the meeting had heard examples of terrible practice. He said: "People being texted to come in to work in the morning only to be turned away when they get there, losing their travel costs and any other arrangements they had made.
"Obviously this would be an impossible situation for anyone with children or people to care for."
He added: "Businesses say they need the flexibility to respond to changing demand, yet it seems these contracts are being used as a way of dodging giving people the security, employment benefits and rights that they deserve. It also allows them to unfairly undercut decent employers who pay the full costs of providing proper employment."
Karen Whitefield, campaigns officer at UDDAW, said: "If major supermarkets can respond to business fluctuations without resorting to zero-hours contracts then why can't many of the businesses that currently use these contracts?"