On Dec. 29, 1890, along the Wounded Knee Creek on the Pine Ridge Reservation in the southwest corner of South Dakota, the U.S. Army killed hundreds of unarmed members of the Lakota Sioux tribe, including many women and children.

In the aftermath of one of the bloodiest acts of violence against Native Americans by federal forces, the government looked into the conduct of the troops of the Seventh Cavalry — and decided to award 20 Medals of Honor, the nation’s highest military commendation, to soldiers involved in the massacre.

Now members of the tribe are stepping up a long-running pressure campaign to have those medals rescinded, saying that the government should recognize the atrocity for what it was and take a step that could help heal the historical wounds of that day.

They recently won support from the State Senate in South Dakota, which passed a resolution in February urging Congress to investigate the award of the medals. On Capitol Hill, supporters of the effort, led by Senators Elizabeth Warren of Massachusetts and Jeff Merkley of Oregon, both Democrats, are hoping to make a new push on behalf of legislation they have sponsored, the “Remove the Stain” bill, that would rescind the medals.

“I believe on our reservation, we have a pervasive sadness that exists here because of what happened at Wounded Knee, the massacre, and it has never been resolved and there has never been closure,” said Marcella Lebeau, a citizen of the Two Kettle Band, Cheyenne River Sioux.

Ms. Lebeau, a 101-year-old veteran who served during World War II as a surgical nurse near the front at the 25th General Hospital in Liège, Belgium, and later worked for the Indian Health Service, is among those pushing for the medals to be rescinded. Ms. Lebeau said she was especially bothered by the fact the country’s most prestigious military decoration was awarded to men who slaughtered women and children.

Many of the award citations noted “gallant conduct in battle” and “distinguished” or “conspicuous” bravery, while documenting few details to justify those characterizations.