Thousands of demonstrators gathered in Charleston for the rally on Monday and heard words of support from Democratic senators Joe Manchin and Jay Rockefeller and Congressman Nick Rahall.

The legislators reaffirmed their stance that the retirees were entitled to keep receiving benefits and that Patriot was breaking a contractual promise negotiated with UMWA to maintain benefits for life.

Building support for their recently introduced bill to use federal funds to cover benefits for retired miners, including those at Patriot, the lawmakers said that if Patriot was successful in shedding its legacy obligations it would set a precedent for other companies to do the same.

"If we don't correct it here in the coalfields of West Virginia, not a worker in America will be protected," Manchin said.

UMWA president Cecil Roberts, West Virginia Governor Earl Ray Tomblin and American Federation of Labor and Congress of Industrial Organizations president Richard Trumka also spoke at the rally before demonstrators marched to Patriot’s West Virginia headquarters.

Sixteen arrests were made among attendance of more than 6000 people, with Roberts and 15 others blocking the building entrance and being arrested on a charge of unlawful assembly.

According to UMWA, retirees from Indiana, Illinois, Kentucky, Pennsylvania, Ohio, Virginia and West Virginia attended the rally and subsequent march, which the union claims to be one of the biggest it has organised.

The union has held several previous protests in St Louis to speak out against Patriot’s plans to rid a $1.6 billion liability for retiree benefits.

Some of those in danger of losing benefits had never worked for Patriot but had signed on with Peabody Coal and Arch Coal.

Peabody Coal spun off Patriot in 2008 and Patriot bought Arch’s Magnum Coal the following year.

Patriot first filed for bankruptcy in July 2012.

The bankruptcy court is scheduled to decide Patriot’s case on April 23.