Two months ago, the RSPCA and Cats Protection made a joint call for cat cafes to be phased out, saying that it was "almost impossible" for them to guarantee the animals' welfare.
本句主干为 "the RSPCA and Cats Protection made a joint call"。"saying that..." 为现在分词短语作伴随状语，说明联合呼吁的同时所表达的内容；其中 "that it was almost impossible..." 为宾语从句，"it" 为形式主语，真正主语是 "to guarantee the animals' welfare"。