No, I don't think so. The US government(s) isn't allowed to punish employees for speech outside of work because of the first amendment.

Google suggests that this is the supreme court case that set that precedent: https://en.wikipedia.org/wiki/Pickering_v._Board_of_Educatio...

That case seems to be about school teachers.

My Dad was a mail carrier for a time in the US. According to his union newsletter, he did not all the full free speech rights outside of work as an average citizen. He was not allowed to talk about work conditions outside of work. He also did not have the right to strike.

I could have the details wrong, this was in a newsletter I read in the 1980s. Oddly, I remember exactly were I was sitting when I read this.

While the case was brought be a teacher the ruling was not limited to teachers.

Can't speak to what your union told your dad. There are some limitations about speech related to work, but that sounds like a more extreme version than I'm aware of being upheld. Can speak to laws about striking even less.

point being teachers are not federal US Government employees, they work for a subdivision of the state. A ruling about teachers seems like it might be not too relevant to Federal workers.

This web pages links to a PDF with a handy flow chart from the ACLU outlining when Federal employee might have restricted speech https://www.acludc.org/en/know-your-rights/know-your-rights-...

It seems hard to tell, given that private sector unions tend towards being at large quasi-governmental corporations. Unions do add difficulty to the firing process, which seems like it should be enough to fend off the employer firing you simply based on not wanting all of the harassing phone calls. But if management and union management still want to go through the process of firing you for what you said, then a government employee would still have the defense that doing so would violate their rights.

The prevalence of public sector unions itself is actually a good example of the trend I'm talking about though!

If you're such a screwup that even your union wants you gone, you'll lose your job, period. Whether it's public or private doesn't matter. Very often the job of a union rep or union legal counsel is to ensure a soft landing. Source: interned with a police union's legal counsel.

One thing to keep in mind about police officers and similarly situated government employees is that maintaining credibility as a court witness is a fundamental requirement of the position. A police officer who's credibility can be easily attacked on the stand has substantially diminished capacity to perform their duties. Part-and-parcel of being any kind of law enforcement officer is testifying to collected evidence on the witness stand.

While the government technically can't retaliate directly for not testifying against yourself in an administrative hearing, failure to be fully forthcoming in such an investigation demonstrates a lack of candor which in turn could be used to impeach you as a witness. If the government has evidence of lack of candor and sufficient motivation to get rid of you, you better start searching for a new job.