"It's time for Congress to put a thoughtful plan in place to increase the minimum wage," McMillon said at the start of the giant retailer's annual meeting in Bentonville, Arkansas. "Any plan should take into account phasing and cost-of-living differences to avoid unintended consequences."
The world's biggest retailer, which employs 1.5 million people in the U.S., has faced increasing pressure to raise its pay. Amazon CEO Jeff Bezos, in his annual letter to shareholders in April, issued a challenge to other retailers, not naming which ones specifically, to match its wages and benefits.
Walmart's minimum wage of $11 an hour, set in January 2018, is still below Amazon's, which was hiked to $15 in November. "Do it! Better yet, go to $16," Bezos said in the letter.
Walmart, however, has said its average, hourly compensation including benefits comes out to be more than $17.50.
Walmart has also been sweetening its perks to include benefits such as the opportunity for employees to pay only $1 a day to earn college degrees in fields related to business and technology.
At Walmart's headquarters, Sanders argued that a $15 per-hour minimum wage "is not a radical idea." He noted Walmart's competitors — Amazon and Target — have started to phase in a $15 per-hour pay floor.
Target will finish phasing in a minimum hourly wage of $13 this month, which puts it on track to reach $15 an hour by the end of 2020.
"It's clear by our actions, and those of other companies, that the federal minimum wage is lagging behind," McMillion said, adding "$7.25 is too low."
Sanders said later that many Walmart workers are relying on public housing and food stamps just to get by.
"The American people are sick and tired of subsidizing the greed of some of the largest and most profitable corporations in this country," the Democratic presidential hopeful said.
Walmart has a market value of about $298 billion. Its shares were up 1.8% Wednesday afternoon, having climbed nearly 12% this year. On a constant currency basis, Walmart's total revenues amounted to $500.9 billion in fiscal 2018, and its operating income was $20.50 billion.