Srimad Bhagavatam Canto 07, Chapter 11, Text 14

SB 7.11.14

rajño vrttih praja-goptur
 aviprad va karadibhih
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
For a brahmana there are six occupational duties. A ksatriya should not accept charity, but he may perform the other five of these duties. A king or ksatriya is not allowed to levy taxes on brahmanas, but he may make his livelihood by levying minimal taxes, customs duties, and penalty fines upon his other subjects.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Visvanatha Cakravarti Thakura explains the position of brahmanas and ksatriyas as follows. Brahmanas have six occupational duties, of which three are compulsory — namely, studying the Vedas, worshiping the Deity and giving charity. By teaching, by inducing others to worship the Deity, and by accepting gifts, the brahmanas receive the necessities of life. This is also confirmed in the Manu-samhita:
sannam tu karmanam asya
 trini karmani jivika
yajanadhyapane caiva
 visuddhac ca pratigrahah
Of the six occupational duties of the brahmanas, three are compulsory — namely, worship of the Deity, study of the Vedas and the giving of charity. In exchange, a brahmana should receive charity, and this should be his means of livelihood. A brahmana cannot take up any professional occupational duty for his livelihood. The sastras especially stress that if one claims to be a brahmana, he cannot engage in the service of anyone else; otherwise he at once falls from his position and becomes a sudra. Srila Rupa Gosvami and Sanatana Gosvami belonged to a very respectful family, but because they engaged in the service of Nawab Hussain Shah — not even as ordinary clerks, but as ministers — they were ostracized from brahminical society. Indeed, they became like Mohammedans and even changed their names. Unless a brahmana is very pure, he cannot accept charity from others. Charity should be given to those who are pure. Even if one is born in a family of brahmanas, if one acts as a sudra one cannot accept charity, for this is strictly prohibited. Although the ksatriyas are almost as qualified as the brahmanas, even they cannot accept charity. This is strictly prohibited in this verse by the word apratigraha. What to speak of the lower social orders, even the ksatriyas must not accept charity. The king or government may levy taxes upon the citizens in various ways — by revenue duties, customs duties, realization of fines, and so on — provided the king is able to give full protection to his subjects to assure the security of their life and property. Unless he is able to give protection, he cannot levy taxes. However, a king must not levy any tax upon the brahmanas and the Vaisnavas fully engaged in Krsna consciousness.
Srimad Bhagavatam Canto 07, Chapter 11, Text 13
Srimad Bhagavatam Canto 07, Chapter 11, Text 15