I've never even been asked for references at any technical job in my life. HR departments generally do make some attempt at verifying employment, doing a background check, etc.

So no, in these cases it's not harder. There's no leverage either way.

Because what do reference letters even mean? How do you know the person writing the letter is even telling the truth? This is somebody you've never met and don't know at all. How do you know they don't unfairly hold a grudge against this ex-employee because they took it personally when they quit? Or how do you know they don't just write glowing references for everyone because they know "it's tough out there" and "everyone deserves a second chance"?

I always assumed this is why I've never been asked for references in my professional career, because the companies I applied to knew that references aren't worth the paper they're written on.