When shopping in a supermarket in Mexico, you are likely to see senior citizens bagging groceries at the checkouts. These seniors are not employees, but volunteers, subsisting entirely on tips.

At Walmart and its subsidiaries Sam’s Club, Bodega Aurrera and Superama and other supermarket chains such as Chedraui, Soriana and La Comercial Mexicana, pensioners bag groceries. None of them receive salaries, but the work is important to them.

Mexico does not have age-based labor discrimination laws. Employers can advertise for a position and include the age range they are willing to hire. Even when these age ranges are not explicitly stated, it is nearly impossible to find a job in Mexico after turning 60. This creates a desperate situation for senior citizens whose pensions do not cover living expenses.

Supermarket chains take advantage of this desperation by hiring them as volunteers instead of employees, at great benefit to their bottom line.

Volunteers at the Superama on Río Churubusco in Mexico City work five-hour shifts, six days a week, with their day off rotating from week to week.

Although they have none of the benefits or protections of regular employees, they are still expected to follow many of the same rules. If they want to go on vacation, they must ask for permission in advance but receive no vacation pay.

If they miss a day of work, they must bring a written justification, such as a doctor’s note. Their only medical insurance is through pensions from their previous careers.

At Superama, volunteers work for 30 minutes, then rest for 30. Not every supermarket provides breaks. At Soriana, volunteers work for five consecutive hours. (The store manager at Soriana División del Norte did not allow me to conduct any interviews or take photos.)

Diego, 66, who asked that we not publish his name, has been bagging groceries at Superama for four years. “I’ll keep working until I fall over. I have to.”

So how are the tips?

“Some people tip better than others. You might get 10 pesos [US $0.50) for two bags, or you might bag a week’s worth of groceries and get a smile, or a blessing.” Diego used to be self-employed but retired with a government pension.

María Guadalupe Zarate, 64, has also been at Superama for four years. She previously worked as the head cashier for the IMSS Social Security Institute, and is also on a government pension. “I can make about 200 pesos a day. That money is important for my personal economy. If I need to rest when it isn’t my break, one of the other volunteers will cover for me,” she said. What she makes in tips is almost double the minimum wage for a day of work in Mexico City — 102.68 pesos.

Walmart has a long history of shady business practices and strained labor relations in Mexico. In March of this year, the company narrowly avoided an 8,000-employee strike by meeting some of their demands. In 2012, the New York Times published an exposé on their history of using bribes to circumvent zoning laws, including opening a store next to the pyramids at Teotihuacán, which led to prolonged protests by local residents.

In 2008, Mexico’s Supreme Court ruled Walmart’s employee payment scheme was unconstitutional. It had been paying employees with vouchers only redeemable in their stores.

The federal government reached an agreement recently with pension funds that will reduce commissions and give a person entering the workforce today 10% more upon retirement. Unfortunately for current retirees, there are no plans to increase their pensions.

Mexico’s senior citizens will have to continue to make ends meet however they can, and for many that will mean bagging groceries for tips.

The writer lives and works in Mexico City.