You do not become one of America's richest families without worrying about your standard of living. Still, they would take a hit. The company had a net profit of $13B last year. Ran the numbers and, if every employee worked 40 hours a week, (not something Walmart is known for doing) with 1.5 Million employees in the US, it would cost them an additional $4.3 Billion of the $13 Billion net profits. That's NET profits, not gross revenues. It would lower their tax liability some, but not enough for their financial folks to be happy. I know locally, thanks to a strong economy at the moment, they've had to raise their pay about $2 an hour in the last 4 years. Still, the cost of living is high enough in this area that a large percentage of those employees still need government assistance.
No they'll keep their standard of living, even though you'll never see one of them working the check out lane anytime soon.