Tess Holliday claims many designers won't loan her clothes.
The 32-year-old plus-sized model admitted some fashion houses don't even "respond" to requests from her stylist to dress her for high-profile events.
She said: "I've been working with my stylist Megan for a couple of years now. She's reached out to designers that I didn't think would dress me.
"I went to Kate Spade's presentation, and Kate Spade dressed me for my book tour. But there are a lot of people that [won't] even respond. Kate Spade was one of the big brands that did."
But Tess was full of praise for Christian Siriano, as she "really appreciates" his "use of diversity".
She told InStyle: "I didn't see anything I wouldn't wear personally.
"Christian's use of diversity is always really appreciated. I was backstage before the show and not only did he have plus size models, but he had a few different races, he had trans models, even his sister walked in the show! It was just was so beautiful.
"If I were to call him tomorrow and say 'I have this event and I need something for it', he would make it."
And Tess has called for more "representation" of bigger women on the runway.
She said: "I'm grateful that some of these designers are at least showing 12 and 14, but I think that it's frustrating because I want it to be available for more plus-size women globally. I want to see more representation, I want to see them doing it in a really thought-provoking way and actually understanding how to dress our bodies.
"And yes, it is complicated, but we're a huge percent of the market and we have so much buying power, and we're just constantly being ignored."