One of our senior (and more competent) engineers, "Peter", who was due for a promotion and pay raise a few months back, raised an issue and meeting with me when his promotion was deferred indefinitely due to COVID. After explaining to him how many companies, even Google, are putting off promotions and raises due to the pandemic, he just retorted with statements like "exceptions are made for exceptional circumstances; I made the company a lot of money" and "how nice, but it seems executives and managers didn't get that memo, as they're getting record bonuses". After explaining how I'm not the one that makes those decisions, I have to threaten him with a formal reprimand to calm him down.
Fast forward a few months: we've noticed a change in the programming languages and technologies being used in our products (i.e. more open source technologies, modern programming languages and methodologies, etc.). Productivity is even up, and Peter seems to be in good spirits, and back to his usual levels of productivity too. All seems well, until we noticed 10x the normal requests from the Legal team for permission to use open source software in our products (not a problem, as long as it doesn't mean we have to give our products away for free). What's odd is that employees are the owners/authors of a lot of these third-party open-source projects.
It turns out Peter spread the word of deferred promotions and raises, and created the impression that if he was denied "his due", most others would likely face the same. So, Peter took it upon himself to encourage teams to make an effort to use new technology that would look good/modern on the CV/resume if employees were laid off. He also led an effort to get overtime to zero, and have employees work on work-related open-source projects in their spare time (i.e. "use GitHub as a secondary resume/CV"). Even though we can use most of the open source software employees have been developing in spare time, we no longer have exclusive ownership of code employees would write as part of overtime to advance within the company.
In short: Peter has taken it upon himself to drive down overtime across the company, and plan projects so the first priority is to buff up the resumes of colleagues and himself.
I can't fire him outright, since there's no material evidence he led this effort, and I'm being urged to try and reclaim/salvage/steer him "back to the light side". I'm permitted to offer up to a 30% one-time bonus (i.e. about 4 months of pay), but he just smirks and says he "doesn't know what I'm talking about". I even overstepped my authority and said "look, this needs to end; I can offer a 50% bonus and let you walk away with your severance package too in order to save face", and he still insists (but smirks) that he's oblivious to the topic. He's now turning down the promotion as well stating "I have no idea what you're talking about, but you and the execs clearly have a poor opinion of me if you're offering money for help with something I don't know about; and the well has been nice and poisoned it seems, in your eyes. I don't see any benefit to continuing these discussions".
Is there any way to steer such an employee (a lot of the engineers trust him, so he seems to have a lot of sway), or do we just rip the bandaid and fire him? Unfortunately, his severance package is large, so I'll be in trouble if we have to pay it out in full.