The most widespread constraint is against two different labial consonants (other than w) occurring together in a root, a constraint which can be found in all branches but Omotic.
ðə mˈoʊst wˈaɪdspɹɛd kənstɹˈeɪnt ɪz ɐɡˈɛnst tˈuː dˈɪfɹənt lˈeɪbɪəl kˈɑːnsənənts ˈʌðɚ ðɐn dˈʌbəljˌuː əkˈɜːɹɪŋ təɡˌɛðɚɹ ɪn ɐ ɹˈuːt, ɐ kənstɹˈeɪnt wˌɪtʃ kæn biː fˈaʊnd ɪn ˈɔːl bɹˈæntʃᵻz bˌʌt ɑːmˈɑːɾɪk.