Wal-Mart workers in 15 U.S. cities staged protests on Thursday, calling for improved working conditions and better wages.

New York police arrested three protesters in New York City as they attempted to deliver a petition to company board member Christopher Williams demanding wages of $13 US an hour. 

The national day of protest was organized by the group Organization United for Respect at Wal-Mart (OURWal-Mart) and came a week after U.S. fast-food workers held similar protests to demand the federal minimum wage be raised.

Currently, workers earn on average $8.81 an hour, according to OURWal-Mart, but many say they are kept on part-time status so the retailer does not have to pay them benefits.

In last week's protest, fast-food workers demanded an increase to the federal minimum wage from the current $7.25 an hour to $15 an hour.

Last week's action was part of a longer-term public campaign calling for a higher minimum wage that would allow U.S. workers to take home at least $25,000 a year.

Workers fired after protesting at shareholder meeting

Thursday's protest was not the first by Wal-Mart workers. In June, 100 Wal-Mart employees protested at a shareholder meeting in Bentonville, Ark. OURWal-Mart claims the retailer has disciplined nearly 80 of those involved in that protest and illegally fired at least 20.

The union-backed group says it has filed more than 100 unfair labour practice complaints against Wal-Mart with the National Labor Relations Board over the firings and disciplinary action.

Wal-Mart denied it had acted illegally and said it fired its employees for missing days of work.

"We're calling on Wal-Mart to allow us better wages, affordable wages, sufficient health care, and to stop silencing workers who are speaking out, such as myself," said Carlton Smith, who worked for Wal-Mart for 17 years before being fired in May.

"We shouldn't be fired for standing up and speaking out."

Labour practices also targeted

Thursday's protests targeted the offices of Wal-Mart board members in New York and San Francisco.

Protests were also planned for Washington D.C., Chicago, Boston, Sacramento, Miami and Dallas.

Lawmakers in the District of Columbia approved a bill in June to boost minimum wage in the district to $12.50 an hour, but Mayor Vincent Gray hasn't said whether he'll let it become law.

Wal-Mart is the largest private employer in the U.S., with a workforce of 1.3 million.

The wage issue isn't the only one of Wal-Mart's policies being publicly debated. The retailer also faces scrutiny over purchasing patterns that favour foreign goods and the labour practices of its suppliers, including the garment factories in Bangladesh that employ low-wage workers in harsh working conditions that drew international critcism earlier this year.

Another Wal-Mart worker, Raymond Bravo, 36, of San Pablo, Calif., said he was fired after taking part in protests in June. Bravo, who said he earned $10.25 an hour as a janitor, said his hours were limited to 30 a week.

He said many of his fellow employees often ran out of money and came to work hungry at the end of every month.

Wal-Mart claims its employees are not underpaid and that its full-time associates make $12.40 an hour. It dismissed the protests in a news release.

"A handful of union orchestrated media stunts, made of up of primarily union members and activists, don't represent the views of the vast majority of the 1.3 million associates who do work for Wal-Mart," the company said.

The company has successfully repelled attempts to unionize its workers.

With files from Reuters