Since most or even all of them are publicly traded companies it isn't that difficult to find out.
Walmart had a net income of 14 billion, they have roughly 2.1 million employees, that leaves each employee with an additional 6.6k for this year or roughly an additional 550 a month.
Doesn't sound a lot but that can be done without impacting any other business practices. And for some of the employees overseas that might be doubling their salaries.