Wal-Mart workers and supporters marched in protest at a number of stores across the United States on Friday, blasting the wages, benefits and treatment of employees of the world's largest retailer.

The efforts seemed to do little to keep shoppers away - Wal-Mart said it was its best post-Thanksgiving sale Friday ever.

In Lakewood, Colorado, dozens of protesters outside a Wal-Mart accused the company of corporate greed and underpaying its workers.

"This is the way you get a fair shake. You've got to fight for it. You've always had to," said protester Charlie May, of the Industrial Workers of the World, a labour organisation.

Shoppers entered the store without incident.

Footage also showed protests taking place on Friday outside Wal-Mart stores in Chicago, Illinois, and Landover Hills, Maryland.

In Paramount, California, authorities arrested a small group of protesters on Friday outside a Wal-Mart.

A union-backed group called OUR Walmart has said that it is holding an estimated 1,000 protests in 46 US states. The exact number is unclear.

Wal-Mart Stores Inc. has rebutted that estimate, saying the figure is grossly exaggerated and that the protests involved few of its own employees.

OUR Walmart, made up of current and former Wal-Mart employees, was formed in 2010 to press the company for better working conditions.

Wal-Mart has criticised the group for relying largely on other unions and non-employees to make up the ranks protesting outside its stores.

The retailer also filed an unfair labour practice charge with the National Labour Relations Board last week against the United Food and Commercial Workers International Union.

The company said that the demonstrations organised by OUR Walmart threatened to disrupt its business and intimidate customers and associates.

Wal-Mart estimated that fewer than 50 associates participated in Thursday and Friday's protests nationwide.

Company spokesman Dan Fogleman said that the number of associates who missed their shifts during the two days of events is 60 percent lower than last year.

The union group estimated that "hundreds" of employees participated nationwide.

Wal-Mart for many years has faced intense scrutiny over its wage and benefit policies and treatment of its workers.

Fogleman says that the company provides some of the best jobs in the retail industry and that its wages and benefits typically meet or exceed those of competitors.

The retailer maintains that it has many long-term employees and that its turnover rate is below the industry average.

At the protest in Landover Hills, Maryland, Wal-Mart store manager Bobby Williams said the company would not retaliate against its workers and would listen to them.

"What I can say is that we would never retaliate against any associates. We will listen to their voices, they have the open door, and we will make sure that we'll always be respectful, and that things are taken care of in an appropriate fashion." Williams said.

Wal-Mart, based in Bentonville, Arkansas, operates 10,400 stores in 27 countries.