In Manu Smriti for example it is said:
2.49 An initiated Brahmana should beg, beginning (his request with the word) lady (bhavati); a Kshatriya, placing (the word) lady in the middle, but a Vaisya, placing it at the end (of the formula).
In Apastamba Sutra 1.1.3:
bhavat pūrvayā brāhmaṇo bhikṣeta || 28 ||
- A Brāhmaṇa shall beg, prefacing [his request] by the word 'Lady'. “Bhavati bhīkṣāṃ dehi!”
bhavat madhyayā rājanyaḥ || 29 ||
- A Kshatriya [inserting the word] 'Lady' in the middle [between the words 'give alms'], “Bhīkṣāṃ bhavati dehi!”
bhavat antyayā vaiśyaḥ || 30 ||
- A Vaiśya, adding the word 'Lady' [at the end of the formula]. “Bhīkṣāṃ dehi bhavati!”
These verses are talking about dvijas who have undergone Upanayana Sanskar, so they would not mention Shudras. However, they don't mention a punishment for non-dvijas begging for alms in this way. Is there one?