In a somewhat surprising turn of events at Walmart's annual investor meeting, CEO Doug McMillon voiced his opinion that the time has come for Congress to raise the minimum wage beyond $7.25 an hour.

"The federal minimum wage is lagging behind," McMillon said at Walmart's annual shareholders meeting in Bentonville, Arkansas on Wednesday (June 5).

There has been no minimum wage increase in the U.S. since 2009.

The comments came as a surprise, and some have speculated that Walmart's status as the nation's largest private employer could create pressure on Congress to act. It could also take some pressure off of Walmart from labor rights groups, who have long been calling on the retailer to raise its in-house minimum wage from $11 an hour.

McMillon went on to note that, given the possibility of unintended consequences, local cost of living differences should factor into how the wage rage is determined. He also said that a hike may need to be phased in over time. Walmart has raised its wages by 50 percent over the last four years, , McMillon noted, and has also expanded its benefits and training opportunities. In some markets, Walmart pays more than $11 per hour as a push to "recruit and retain the talent we need to run a good business,” he added.

Some, however, believe McMillon has not gone far enough. In a hotel ballroom around the corner from Walmart's shareholders meeting, presidential candidate Bernie Sanders criticized McMillon's $24 million annual salary, and called Walmart's pay "starvation wages."

"Walmart can afford to pay its employees a living wage of at least $15 an hour," he pointed out.

Walmart is a recent addition to the wave of mega-retailers rethinking their historic opposition to minimum wage hikes. McDonald's announced in March that it would no longer lobby against them. Amazon has raised its minimum pay to $15 an hour, and challenged its top retail competitors to do the same.