'Their right is to say, 'Thanks, but no thanks,' and walk away,' said Bryant.

And if no consent is provided, he said, customers are under no obligation to comply. Michael Bryant, CCLA's executive director and general counsel, said retailers should get consent before checking receipts or bags. The Canadian Civil Liberties Association (CCLA) said it's investigating the practice of retailers doing routine security checks at the exit, concerned that the way they're conducted may jeopardize customers' rights. She said her local Walmart increased its checks in the spring. 'It was not a request, it was a demand,' said Penny Rintoul of Vaughan, Ont., about a recent receipt check just before she exited Walmart with her purchases.

An apparent step-up of receipt and shopping bag checks at Walmart has sparked customer complaints, raising concerns about shoppers' rights.