Monika Miczura Juhasz, known as Mitsou, calls herself “an internationally acclaimed Hungarian Roma singer”. She claims that Beyoncé has stolen her voice for the first 13 seconds of the song. She became aware of it when friends started calling her after hearing the “a capella solo”.
All together, Mitsou’s vocals are featured for over one and a half minutes of the five and a half minute song. The original recording of the traditional Roma song, called “Bajba, Bajba Pelem,” was released under the title “Gypsy Life on the Road” by North Pacific Records in 1997.
She’s seeking unspecified damages.
Source, summarized by me.