* Retailers including Amazon and Wal-Mart stop selling flag
* Hundreds chant "Take it down" as lawmakers vote to open debate
* Calls for Mississippi to remove Confederate symbol from its flag
* Virginia stops allowing rebel flag on license plates (Adds second flagmaker halting production of Confederate emblem, Georgia to reconsider license plate design)
By Harriet McLeod
COLUMBIA, S.C., June 23 (Reuters) - An initiative to remove the Confederate flag from the South Carolina State House grounds picked up steam on Tuesday, a week after the massacre of nine black church members, and criticism over the emblem long associated with slavery spread to other U.S. southern states.
U.S. retailers joined lawmakers in distancing themselves from the banner, with industry leaders Amazon.com Inc and Wal-Mart Stores Inc pulling the images of the rebel flag from their stores and websites, joining Google Inc , Sears Holdings Corp and eBay Inc .
The Civil War-era flag of the South's pro-slavery Confederacy has become a lightning rod for outrage over the shootings in Charleston, South Carolina, which authorities say was motivated by racial hatred.
In Columbia, the capital of South Carolina, hundreds of people chanted "Take it down," while state lawmakers voted on Tuesday to open debate on removing the Confederate flag from the State House grounds.
Dylann Roof, a 21-year-old white man charged with nine counts of murder for the shooting at the church last Wednesday, had posed with a Confederate flag in photos posted online with a racist manifesto.
'TO FOSTER RACIAL UNITY'
Just hours after politicians in several southern states began calling for the removal of the Confederate flag on Monday, some of the nation's largest retailers announced they were halting sales of related merchandise.
Prominent U.S. flag makers said on Tuesday they would stop manufacturing and selling Confederate flags.
"We hope that this decision will show our support for those affected by the recent events in Charleston and, in some small way, help to foster racial unity and tolerance in our country," the Pennsylvania-based Valley Forge Flag company said in a statement.
The debate over the rebel flag spread to other southern states on Tuesday.
In Mississippi, the state which still most prominently incorporates the "Stars and Bars" in its flag, Speaker of the House Philip Gunn became the first Republican in state history to publicly support a flag change when he called the Confederate emblem "a point of offense that needs to be removed."
Virginia, which was also part of the Confederacy, will no longer allow special vehicle license plates for the Sons of Confederate Veterans group that feature the flag, Governor Terry McAuliffe said on Tuesday. Georgia's governor said he would seek to redesign a similar license plate in his state.
Opponents of the flag consider it an emblem of slavery, racism and U.S. xenophobia. Supporters say it represents the South's heritage and culture, as well as a memorial to Confederate casualties during the 1861-65 Civil War.
MORE COMPLEX ISSUE, CRITICS SAY
Critics said the Confederate flag, while powerful in its symbolism, was perhaps a far simpler matter to address than the far more complex U.S. issues of racism, discrimination against African Americans and inequality.
As the Confederate flag fluttered only yards away on the grounds of the South Carolina State House, a crowd of about 1,000 listened to politicians and civil rights leaders voice their support for taking down the battle flag.
"Anyone who gets in front of this train is going to get run over," said Leon Howard, a state legislator, referring to the political momentum gathering behind the initiative.
Until recently Republican Governor Nikki Haley of South Carolina had been unwilling to discuss the flag.
"The change in opinion in the last day or two is like nothing I have ever seen. It's been a tidal wave," said College of Charleston political science professor Gibbs Knotts.
The crowd heard prayers offered in the memory of State Senator Clementa Pinckney, a longtime advocate of the flag's removal. Pinckney, pastor of the Charleston church, was one of the shooting victims. President Barack Obama will attend his funeral on Friday.
The Confederate flag controversy is the latest flashpoint in a year of intense debate over U.S. race relations, sparked by the killings of unarmed black men by police officers in Ferguson, Missouri; New York City; and Baltimore. The outcry has spawned a reinvigorated civil rights movement under the "Black Lives Matter" banner.
Governor Haley threw her support behind removing the flag on Monday. She called on lawmakers, whose legislative year wraps up this week, to address the issue over the summer and said she would order a special session if they did not.
It would take a two-thirds majority vote by both chambers of the legislature to undo the state law that requires the flag to fly at a memorial to Confederate soldiers on the State House grounds.
That law was the result of a 2000 compromise that removed it from atop the State House, where it was first put up a half century ago at the peak of resistance to federal efforts to end segregation in the South.
(Additional reporting by Emily Le Coz in Jackson, Mississippi and David Adams in Miami; Writing by Frank McGurty and Howard Goller; Editing by James Dalgleish and Lisa Shumaker)