This study examines ERP correlates of the different processes associating two phones to one vs. two phonemic categories in two regional varieties of French. Two groups of French listeners are compared, respectively exploiting two regional varieties, with a contrast between the mid-low /ɛ/ and the mid-high /e/ for Northern French (NF) but not for Southern French (SF). It is expected that the competition between the two close categories /e/ vs. /ɛ/ in NF could induce an ERP modulation in the processing of /ɛ/ compared to a phoneme /a/ with no close competitor, serving as control. In contrast, there should be no difference in ERP response in /ɛ/ vs. /a/ in SF, where there is no competition between the close neighbors /e/ and /ɛ/. The participants of the two groups listened to words containing either /ɛ/ or /a/ in a go/no-go semantic categorization task in which the critical /ɛ/ and /a/ words did not require an overt behavioral response. We found a significant difference in the N400 amplitude between the two conditions in the NF but not in the SF variety. The fact that the ERP modulations appear on the N400 component suggests that lexical access is influenced by the regional variety of the speakers.