The Department of Justice has opened a human trafficking investigation into the case, and US Congressman George Miller has demanded detailed documentation about the case from Secretary of Labour Elaine Chao.

The ranks of the workers' allies and supporters have surged during the eight-day journey, and now include several civil rights leaders, the organisers said.

"The attempts to intimidate human trafficking survivors as they have walked in the footsteps of US freedom fighters have failed," said New Orleans Workers' Centre for Racial Justice director Saket Soni.

"... we will demand that Indian Ambassador Ronen Sen take the epidemic of labour trafficking seriously, and help workers and advocates unmask the US federal guest worker programme as a legalised form of servitude."