SB 3.30.33

kevalena hy adharmeṇa
 kuṭumba-bharaṇotsukaḥ
yāti jīvo ’ndha-tāmisraṁ
 caramaṁ tamasaḥ padam
Synonyms: 
kevalena — simply; hi — certainly; adharmeṇa — by irreligious activities; kuṭumba — family; bharaṇa — to maintain; utsukaḥ — eager; yāti — goes; jīvaḥ — a person; andha-tāmisram — to Andha-tāmisra; caramam — ultimate; tamasaḥ — of darkness; padam — region.
Translation: 
Therefore a person who is very eager to maintain his family and kinsmen simply by black methods certainly goes to the darkest region of hell, which is known as Andha-tāmisra.
Purport: 

Three words in this verse are very significant. Kevalena means “only by black methods,” adharmeṇa means “unrighteous” or “irreligious,” and kuṭumba-bharaṇa means “family maintenance.” Maintaining one’s family is certainly the duty of a householder, but one should be eager to earn his livelihood by the prescribed method, as stated in the scriptures. In Bhagavad-gītā it is described that the Lord has divided the social system into four classifications of castes, or varṇas, according to quality and work. Apart from Bhagavad-gītā, in every society a man is known according to his quality and work. For example, when a man is constructing wooden furniture, he is called a carpenter, and a man who works with an anvil and iron is called a blacksmith. Similarly, a man who is engaged in the medical or engineering fields has a particular duty and designation. All these human activities have been divided by the Supreme Lord into four varṇas, namely brāhmaṇa, kṣatriya, vaiśya and śūdra. In Bhagavad-gītā and in other Vedic literatures, the specific duties of the brāhmaṇa, kṣatriya, vaiśya and śūdra are mentioned.

One should work honestly according to his qualification. He should not earn his livelihood unfairly, by means for which he is not qualified. If a brāhmaṇa who works as a priest so that he may enlighten his followers with the spiritual way of life is not qualified as a priest, then he is cheating the public. One should not earn by such unfair means. The same is applicable to a kṣatriya or to a vaiśya. It is especially mentioned that the means of livelihood of those who are trying to advance in Kṛṣṇa consciousness must be very fair and uncomplicated. Here it is mentioned that he who earns his livelihood by unfair means (kevalena) is sent to the darkest hellish region. Otherwise, if one maintains his family by prescribed methods and honest means, there is no objection to one’s being a family man.