“They do nothing to earn what they receive, they do not even have to ask for it – it comes to them of itself, their only care is to dispose of it. They live in palaces, they riot in luxury and extravagance – such as the no words can describe, as makes the imagination reel and stagger, makes the soul grow sick and faint. They spend hundreds of dollars for a pair of shoes, a handkerchief, a garter; they spend millions for horses and automobiles and yachts, for palaces and banquets, for little shiny stones with which to deck their bodies. Their life is a contest among themselves for supremacy in ostentation and recklessness, in the destroying of useful and necessary things, in the wasting of labor and the lives of their fellow-creatures, the toil and anguish of the nations, the sweat and tears and blood of the human race!”
The preceding passage from The Jungle is given by an orator who delivers a passionate harangue regarding labor rights, human rights and class struggle. I do not know whether Thorstein Veblen had any influence on Upton Sinclair with regards to conspicuous consumption, but Sinclair certainly outlines the frustration and anger the lower, in addition to, working class felt towards the upper class. The Jungle was published in 1906, while The Theory of the Leisure Class was published several years before it in 1899. A Google search didn’t result in any connections, but both men’s names did appear as notable progressives during the progressive era.