(Reuters) — Walmart plans to phase out the sale of eggs from caged hens by 2025.

Walmart, the largest grocer in the United States with control of a quarter of the market, said it would require that egg suppliers adopt an industry standard for treatment of hens by 2025 and have their compliance monitored by a third party.

The new guidelines will apply to the discount retailer’s more than 5,000 stores in the United States, including its Sam’s Club warehouse chain.

Walmart had indicated that it planned to switch to cage-free eggs in May when it announced that it would push its suppliers to adhere to the “five principles” of animal welfare, which include ensuring animals are not starved, have sufficient space to move and do not suffer mental distress.

The company joins McDonald’s Corp, which set a deadline of 2025, and Burger King, which has committed to going 100 percent cage-free for its eggs by 2017.

Walmart said it has offered some cage-free eggs in its stores since 2001.

The move will likely add to pressure on the egg industry, which is facing a costly transition to a cage-free environment.

Only six percent of U.S. hens, or 18 million birds, are now raised without cages, according to a recent estimate by United Egg Producers.