After Fanning, 21, took to Instagram to inform her fans she had collapsed at the Chopard Trophee dinner earlier this week because her "time of the month" interfered with the size of the dress, Jamil condemned the fashion industry's sample size culture, reports dailymail.co.uk.
Pointing out the star's slender frame, Jamil, 33, took to Twitter to say that Fanning shouldn't be "blaming herself for being a few pounds heavier", instead she should be horrified at the dress.
"Jesus Christ, reading about Elle Fanning, a very thin actress fainting because her sample size Prada dress was too tight, and then blaming it on her period, rather than the fact that sample sizes are f*cking insane these days... is symptomatic of a huge problem in fashion," Jamil posted.
"Incredibly slender Elle shouldn't be blaming herself for being a few pounds heavier on her period. She should be horrified at the size of the dress," she added.
Jamil made it clear that she was not "hitting out at Elle Fanning, but at the fashion industry for making a grown woman faint in their clothing".
This came after news that Fanning blamed her tight dress after fainting at the dinner.
The actress, who is a member of the Cannes jury this year, was seated at a table with her sister Dakota, 25, when she fainted and fell off her chair. Dakota quickly helped her up before security whisked them away.
( With inputs from IANS )