The New York fundraiser takes place on 4 May as protests target lead donors and honorary co-chairs Jeff Bezos and Lauren Sánchez.
Elle said Zendaya is stepping back after two press tours, while Streep's representative said she has long been invited but never attended.
The boycott campaign criticises Amazon ties and breaks with fashion-house sponsorship precedent, though Anna Wintour has defended Sánchez and other stars are still expected to attend.
With stars like Meryl Streep boycotting, can the Met Gala survive its controversial new alliance with tech billionaires?
When cultural icons boycott tech titans over ethics, who truly holds the power to shape public opinion?