Yes, there are a few instances in both Taittirīya Saṃhitā and Brāhmaṇa (attached to Kṛṣṇa Yajurveda) and the Śatapatha Brāhmaṇa (Śukla Yajurveda) where it's said śūdras are not fit to conduct yajñas and that brāhmaṇas and kṣatriyas are superior to other varṇas (vaiśyas and śūdras).
Taittirīya Saṃhitā (Kṛṣṇa Yajurveda) on śūdras:
Prajapati desired, 'May I have offspring.' He meted out the Trivrt from his mouth. After it the god Agni was created, the Gayatri metre, the Rathantara Saman, of men the Brahman, of cattle the goat; therefore are they the chief, for they were produced from the mouth. From the breast and arms he meted out the Pañcadaśa Stoma. After it the god Indra was created, the Tristubh metre, the Brhat Saman, of men the Rajanya, of cattle the sheep. There fore they are strong, for they were created from strength. From the middle he meted out the Saptadaśa Stoma. After it the All-gods as deities were created, the Jagati metre, the Vairupa Saman, of men the Vaiśya, of cattle cows. Therefore are they to be eaten, for they were created from the receptacle of food. Therefore are they more numerous than others, for they were created after the most numerous of the gods. From his feet he meted out the Ekavinśa Stoma. After it the Anustubh metre was created, the Vairaja Saman, of men the Śūdra, of cattle the horse. Therefore the two, the horse and the Śūdra, are dependent on others. Therefore the Śūdra is not fit for the sacrifice, for he was not created after any gods. Therefore they depend on their feet, for they were created from the feet. The Trivrt is the breaths; the Pañcadaśa the half-months; the Saptadaśa Prajapati; these worlds are three; the Ekavinśa is the sun yonder. In this they rest, in this they find support. He who knows thus rests on this, finds, support in this.
Śatapatha Brāhmaṇa (Śukla Yajurveda) on śūdras and women:
31. And whilst not coming into contact with Śūdras and remains of food; for this Gharma is he that shines yonder, and he is excellence, truth, and light; but woman, the Śūdra, the dog, and the black bird (the crow), are untruth: he should not look at these, lest he should mingle excellence and sin, light and darkness, truth and untruth.
Some more pointers from Taittirīya and Śatapatha Brāhmaṇas, from A. C. Banerjea's Studies In The Brāhmaṇas:
As far as social groups are concerned, the situation is fairly simple,
and the facts may be stated in outline. In the Śatapatha appears the
off-quoted statement: 'the Varṇas are four; the Brāhmaṇa, the Rājanya,
the Vaiśya and the Śūdra: (catvāro vai varṇāḥ; brāhmaṇo rājanyo
vaiśyaḥ śūdro)'. It is significant that 'jāti' in the later sense of
'caste' is not known to the Brāhmaṇas, and it is difficult to decide
whether 'varṇa' in these texts is better applicable to 'class' or
'caste'. We find, however, that the Ṛgvedic division of 'varṇa' into
the 'ārya' and the 'dāsa' is replaced here by that of the Ārya or the
Daivya and the 'asurya'. In the context of the Mahāvrata, the symbolic
striving of the Ārya (or Arya) and the Śūdra on a piece of a round
hide, results, according to the Tāṇḍya (V.5,14) in the victory of a
member of the Arya caste (śūdrāryau carmaṇi vyāyacchete tayor āryaṃ
varṇam ujjāpayanti). The Taittirīya (I.2,6.7), in the same context
states that the Brahman represents the divine Varṇa, and the Śūdra
that associated with the Asuras (daivyo vai varṇo brāhmaṇaḥ asuryaḥ
śūdraḥ) and in the struggle the Brahman is victorious (brāhmaṇaḥ
Among these four varṇas, the eminence of the Brahman, and the
servility of the Śūdra are fully established. The Taittirīya ('ete
vai devāh pratyakṣaṃ yad brāhmaṇāḥ') refers to the Brahmans as
veritable gods. The Śatapatha mentions them as 'human gods'
(manuṣyadeva). The woman, Śūdra, the dog and the blackbird are,
according to the latter, 'untruth', and are not to be seen (anṛtaṃ
strī śūdraḥ sva kṛṣṇaḥ śakunis tāni na prekṣate). It again
prescribes non-communication with a Śūdra for the consecrated,
stating that, should there be occasion for him to converse with a
Śūdra, let him say to one of these (the Brahman, Rājanya and Vaiśya)
'Tell this one so and so' ('yadi enaṃ śūdreṇa saṃvādo vinded eteṣam evaikam brūyād imam iti vicakṣv enam iti'; ŚB 3:1:1:10). The Aitareya lays down that the 'Brahman is
higher than the kṣatriya' (bhuyān vai brāhmaṇaḥ kṣatriyād), and the
Śūdra is 'the servant of another, to be removed and beaten at will'
(anyasya preṣyaḥ kāmotthāpyo yathā-kāma-vadhyo).
The Rājanya and the Viś or Vaiśya are mutually interdependent. It is
usually the Rājanya who subordinates the Vaiśya, as the latter is said
to be subservient and not refractory to the nobility (kṣatrasyaiva tad
viśam kṛtānukarāṃ anuvartamānaṃ karoti). Further, in the Aitareya, the
Vaiśya-like progeny of the Kṣatriya who drinks curds, is described as
'anyasya balikṛt' (a tributary to another), 'anyasyādyaḥ' (to be lived
upon by another) and 'yathākāmajeyaḥ' (to be oppressed at will).
According to the Tāṇḍya, however, 'the Rājan' (king or Kṣatriya) is
the child (embryo) of the Viś (people or Vaiśya), (viḍ vai saptadaśas
tasyā rāja garbho), who could expel him (aparuddha-rājanya). This
implies that the peasantry was sometimes more powerful than the