SB 11.17.47
sidan vipro vanig-vrttya
panyair evapadam taret
khadgena vapadakranto
na sva-vrttya kathañcana
Translation:
If a brahmana cannot support himself through his regular duties and is thus suffering, he may adopt the occupation of a merchant and overcome his destitute condition by buying and selling material things. If he continues to suffer extreme poverty even as a merchant, then he may adopt the occupation of a ksatriya, taking sword in hand. But he cannot in any circumstances become like a dog, accepting an ordinary master.
Purport:
Sva-vrttya, or “a dog’s profession,” refers to the sudras, who cannot live without accepting a master. A destitute brahmana who is suffering intolerably may become a merchant and then a ksatriya but may never take the position of a sudra by working in a company or accepting a master. Although a ksatriya is ordinarily considered more elevated than a vaisya, the Lord here recommends that distressed brahmanas first accept the vaisya occupation, since it is not violent.