The union, which provided the statements and arranged for the interview with Ms. Gay, says that changing the return policy is among its top priorities as it negotiates with Macy’s for a new contract by Wednesday.

In an email, a Macy’s spokesman, Jim Sluzewski, called the company’s return policy “fair and equitable” to employees. A spokeswoman for Nordstrom, Tara Darrow, said in an email that “we provide our employees with a commission agreement when they are hired that explains how we calculate commissions, and they can always get a copy of the commission agreement.”

For decades, department stores have used commission as a way to motivate employees. Hone your sales skills, help customers and you, too, can share in the rewards. Returned merchandise has also long counted against an employee’s sales, which are used to calculate commission.

Such policies help protect retailers from some legitimate concerns. For example, it prevents an employee from trying to game the system by selling a product to a friend, knowing the product will be returned after a commission is paid. Mark A. Cohen, director of retail studies at Columbia Business School, said companies’ commission policies can help stop employees from overselling products that consumers would be more likely to bring back anyway.

“It may create a distortion over a period of time,” he said of the variable paychecks. “But at the end of the day, the sales associate is being compensated for their net sales, and that is a typical practice.”

Still, the surge of returns has changed the dynamic. Online retailers, many of which have made generous return policies a prime selling point to shoppers — and which do not pay employees based on commissions — have led the push. Amazon, the world’s largest virtual merchant, and many other e-commerce sites offer flexible and sometimes free returns.

“Online-only retailers have conditioned consumers to be able to touch and feel products and then return them if they change their minds, hassle-free,” Kevon Hills, vice president for research at StellaService, a customer research firm, said in an email.