Minimum wage increases will prompt Walmart Stores Inc to adjust base salaries at 1,434 stores, impacting about a third of its U.S. locations, according to an internal memo.

The retailer's memo, sent to store managers earlier this month, offers insight into the impact of minimum wage hikes in 21 states due to come into effect on or around Jan. 1, 2015, according to Reuters.

These are adjustments that Walmart and other employers have to make each year, but growing attention to the issue has expanded the scope of the change. Thirteen U.S. states lifted the minimum wage in 2014, up from 10 in 2013 and 8 in 2012.

Walmart spokeswoman Brooke Buchanan said the company was making the changes to "ensure our stores in the 21 states comply with the law."

For Walmart — the biggest private employer in the U.S. with 1.3 million workers — minimum wage legislation is not a small thing. The company’s operating model is built on keeping costs under close control as it attracts consumers with low prices and operates on tight profit margins.

In recent years, it has been struggling to grow sales after many lower-income Americans lost jobs or income in the financial crisis.

The Walmart memo shows that there will be changes to its pay structure, including a narrowing of the gap in the minimum premium paid to those in higher skilled positions, such as deli associates and department supervisors, over lower-grade jobs.

Walmart will also combine its lowest three pay grades, which include cashiers, cart pushers and maintenance, into one base rate.

The changes appear in part to be an effort to offset the anticipated upswing in labor costs, according to a manager who was implementing the changes at his store.

"Essentially that wage compression at the upper level of the hourly associate is going to help absorb that cost of the wage increase at the lower level," said the manager, who spoke on condition of anonymity.