SB 7.11.14

viprasyādhyayanādīni
 ṣaḍ-anyasyāpratigrahaḥ
rājño vṛttiḥ prajā-goptur
 aviprād vā karādibhiḥ
Synonyms: 
viprasya — of the brāhmaṇa; adhyayana-ādīni — reading the Vedas, etc; ṣaṭ — six (to study the Vedas, to teach the Vedas, to worship the Deity, to teach others how to worship, to accept charity and to give charity); anyasya — of those other than the brāhmaṇas (the kṣatriyas); apratigrahaḥ — without accepting charity from others (the kṣatriyas may execute the five other occupational duties prescribed for the brāhmaṇas); rājñaḥ — of the kṣatriya; vṛttiḥ — the means of livelihood; prajā-goptuḥ — who maintain the subjects; aviprāt — from those who are not brāhmaṇas; — or; kara-ādibhiḥ — by levying revenue taxes, customs duties, fines for punishment, etc.
Translation: 
For a brāhmaṇa there are six occupational duties. A kṣatriya should not accept charity, but he may perform the other five of these duties. A king or kṣatriya is not allowed to levy taxes on brāhmaṇas, but he may make his livelihood by levying minimal taxes, customs duties, and penalty fines upon his other subjects.
Purport: 

Viśvanātha Cakravartī Ṭhākura explains the position of brāhmaṇas and kṣatriyas as follows. Brāhmaṇas 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 brāhmaṇas receive the necessities of life. This is also confirmed in the Manu-saṁhitā:

ṣaṇṇāṁ tu karmaṇām asya
 trīṇi karmāṇi jīvikā
yajanādhyāpane caiva
 viśuddhāc ca pratigrahaḥ

Of the six occupational duties of the brāhmaṇas, three are compulsory — namely, worship of the Deity, study of the Vedas and the giving of charity. In exchange, a brāhmaṇa should receive charity, and this should be his means of livelihood. A brāhmaṇa cannot take up any professional occupational duty for his livelihood. The śāstras especially stress that if one claims to be a brāhmaṇa, he cannot engage in the service of anyone else; otherwise he at once falls from his position and becomes a śūdra. Śrīla Rūpa Gosvāmī and Sanātana Gosvāmī 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 brāhmaṇa 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 brāhmaṇas, if one acts as a śūdra one cannot accept charity, for this is strictly prohibited. Although the kṣatriyas are almost as qualified as the brāhmaṇas, 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 kṣatriyas 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 brāhmaṇas and the Vaiṣṇavas fully engaged in Kṛṣṇa consciousness.