Research on code-switching (CS), the spontaneous alternation between two or more languages within a discourse, remains relatively new and often limited by the use of elicited production tasks, with some exceptions leveraging naturalistic corpora. This study analyses the effects of language directionality and part-of-speech (POS) tags on Spanish-English CS production between corpus modalities and speech communities. We use data from two spoken corpora: Miami Bangor Corpus (MBC; N = 261,711) and Spanish in Texas Corpus (STC; N = 416,784), as well as the written LinCE Corpus (N=278,093). Bootstrap analyses indicate that Spanish serves as the matrix language (i.e., the most used) for MBC and LinCE, while English is for STC. Logistic regression analyses show that the particle-coordinating conjunction combination was the strongest POS predictor of a CS. The results suggest that corpus modality and the speech community affect matrix language proportions and that both previously attested and unseen POS combinations modulate the production of Spanish-English CS.