The "Queen" actor said watching a film in a cinema hall is considered a "communal" experience and feels the expansion of the digital platform poses danger to the theatres.
"It's devastating for people like my husband, film directors, because they want their movies to be watched in a cinema with a group of people," Mirren told Total Film magazine.
"An audience, a movie, and you're all in it together. You're frightened, you laugh, you cry all together. So it's a communal thing. And that's beginning to disappear," she added.
The 72 year-old actor is married to Taylor Hackford, best known for 2004 biopic "Ray".
The 12-day festival, which starts from May 8, has made it mandatory for films to be released in French theatres in order for them to become eligible for the main competition.
Following the rule change, the streaming giant refused to showcase its films in cinema halls and pulled them out of the festival.
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