In a statement, Vedanta said the plant was attacked and property damaged. About 100 people had broken into the plant and ransacked offices.
Mr Subrat Kumar Sahu, a unionist, said the cause of the trouble were workers demanding to be paid after their wages were witheld.
When workers were denied their arrears, they protested and some damage was caused to plant property.
The stoppage at Lanjigarh comes on the heels of the Indian government's notification making it mandatory to obtain environment clearance for projects that undertake major changes in their process line.
Vedanta Aluminium is conducting an expansion programme to raise capacity from 1Mt to 6Mt/y.