Wal-Mart Stores Inc said on Tuesday it was aiming to phase out the sale of eggs from caged hens by 2025, becoming the largest and most influential food retailer to set a deadline for switching to cage-free eggs.

Wal-Mart, 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.

Wal-Mart had flagged 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, a set of guidelines that includes ensuring animals are not starved, have sufficient space to move, and do not suffer mental distress.

Tuesday's announcement makes Wal-Mart the latest retailer to put a firm timetable on the change, joining the likes of 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.

The Humane Society predicted Wal-Mart's move would effectively mark the end of the use of cramped cages, citing the retailer's size and purchasing power.

"This announcement will likely benefit more animals than any other corporate announcement in the history of the animal protection movement," the organization said in a statement.

Wal-Mart 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 about 18 million birds, are currently raised without cages, according to a recent estimate by trade group United Egg Producers.