The reason seems to be that UNRWA is replacing the old food voucher system with one that uses magnetic cards.
I have not seen anything that says that the benefits have changed but these "popular committees" depend on regular outbursts of anger in order to justify their existence. So they are telling residents of the camps that their benefits are being reduced by UNRWA and that the "right of return" is being taken away, and calling on them to strike.
Of course, these regular outbursts against UNRWA are almost never reported in English-language media.
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