A prominent union organizer in Bangladesh was tortured and murdered last week in retaliation for his work in exposing unsafe conditions at garment factories, according to Worker Rights Consortium (WRC), an international monitoring group.

Aminul Islam was a senior organizer for the Bangladeshi Center for Worker Solidarity (BCWS) who was helping organize garment workers employed by the Shanta Group, a company that manufactures clothing for American companies that include Tommy Hilfiger, Nike and Ralph Lauren.

Islam helped ABC News arrange interviews with survivors a a recent deadly factory in Bangladesh, which resulted in a "Nightline" report on designer Tommy Hilfiger's clothing line.

"All indications are that Aminul’s murder was in retaliation for his labor rights advocacy," according to a statement released by the WRC. "This depraved act signals the deterioration of an already grim labor rights situation in Bangladesh, which is now the fourth largest exporter of apparel to the U.S."

The WRC and other groups are urging the government of Bangladesh to conduct an investigation into Islam's death and to end what they say are its attacks on labor rights advocates.

Since large-scale worker protests in 2010 over .11 an hour wages and dangerous working conditions, the WRC says the government and security forces of Bangladesh have been carrying out a campaign of harassment, intimidation and violence against BCWS and other labor rights advocates. Ismal and two other leaders of BCWS – Kalpona Akter and Babul Akhter – were arrested, jailed and beaten in 2010.  

Bangladesh is a leading exporter of university logo apparel and is now the fourth largest producer of apparel for the US market. There are currently 3.6 million apparel workers in the country.

"Thus, the grim labor rights environment in Bangladesh is an issue of enormous importance, for the university apparel sector and beyond," says the WRC.

Nearly 500 workers have died in workplace fires in Bangladesh over the past five years.