Matty Healy was called out in a big way this weekend ... getting dragged across the coals by none other than one of his fellow labelmates, who put him on blast at Glastonbury.

Singer Rina Sawayama didn't mention Matty by name Saturday during her set, but there's simply no question who she was referring to as she was leading up to her song, 'STFU.'

Before going in on the first verse, she said ... "I wrote this because I was sick & tired of these micro-aggressions. This goes out to a white man that watches Ghetto Gaggers & mocks Asian people on a podcast. He also owns my masters! I've had enough!"

The crowd started losing it ... and Rina then launched into a passionate performance.

Of course, people on Twitter were even more turned up ... not only is she trending right now, but Matty is as well -- and people are giving her kudos for calling out what many have labeled problematic behavior of his for a good while, especially as it pertains to race.

The reference to "ghetto gaggers" comes from a podcast Matty appeared on earlier this year -- where he cracked jokes about watching the porn site .. which many considered insensitive.

Not just that ... but he was also yukking it up with the podcast hosts as they mocked Asian accents, all while disparaging Ice Spice. Matty was laughing along to the whole thing -- and he's been getting called out for that as well ... especially amid his romance with Taylor Swift.

Many of Taylor's fans didn't approve of her relationship with him ... and were calling on her to dump the dude. Big picture, the feeling was that he wasn't good for her squeaky clean brand.

As we reported ... the two of them broke up last month after about a month and change of seeing each other. We'd also heard the podcast controversy didn't play a factor in the split.

TS is still touring and getting on with things, and ditto for Matty -- who's been performing with his band, The 1975. All the backlash he'd been facing up until that point had mostly fizzled out -- that is, until Rina here brought it back up again ... in passionate terms, no less.

As for her claim about him owning her masters -- it's unclear what she's getting at. Yes, The 1975 was also signed to her label, Dirty Hit, but there's no indication, publicly at least, that Matty's a label head there. Perhaps Rina's aware of something the rest of us aren't.

It's interesting that Rina's got beef over her masters -- 'cause you know who else famously did too ... Taylor Freakin' Swift.