Ask HN: Can I vendor a GNU GPL package into a MIT project?

I'm helping maintain a moderately popular open-source project, and we have a pull request which requires that we vendor a single file which is licensed GNU GPL.

No modifications will be performed to the GPL file itself, but it will be dynamically required every-time our open-source package is loaded. We don't distribute any binaries, only source code.

I have no idea how GPL copyleft works.

Will including a single GPL file in the MIT project cause the entire project to be GPL?