To challenge this informal warning at work?

[PaperwhiteTheGhost]

Short version: manager told me today I'll be receiving an informal warning- a letter- from HR for discussing my salary. I want to challenge this as it as 1- it's illegal to prohibit employees from disclosing their salary and 2- I don't think there is an issue with it either.
However, it is an informal warning that doesn't go on my file and my manager is of the opinion that it's inconsequential and not worth bothering to challenge.
What would you do?

More info if required: I am a registered healthcare professional working for a private company but in the public sector. My role is equivalent of NHS band 6.

My salary is pretty average and works out roughly to what I'd be earning at the top of NHS band 6- I am paid a flat rate salary which is comparable to band 6 NHS salary with shift/antisocial hours allowance and London Weighting added. We don't get any extras aside from planned overtime.

I have only ever mentioned my salary in passing when it has come up in context of general conversation.

As far as im aware, there was no complaint about me, rather another employe asked why they weren't paid as much as me which annoyed the head of department who took it to HR.

If you’re a nurse you must be part of the RCN, they can help with things like this

They're entitled to write you a 'letter of concern', basically a written telling off that they keep on file. You are entitled to write back saying that you were within your rights to disclose your salary and at no point were you asked to keep it confidential, and insist that letter also goes on file.
While the letter isn't a disciplinary sanction, personally I'd not let it go without response, as it can be used as part of the big picture if there's future issues. Especially if they word it in terms of 'disclosing confidential information' or some other vague phrase that implies wrong doing.
You other option as you can't appeal it is to put in a grievance that you have been treated unfairly.

Hi op, this is upsetting.
So the head of department is the problem, dodgy judgement and inclined to be punitive.

Hr will be perfectly aware you are allowed to discuss salary.

Please do ask them about which policy this is mentioned in, get it all in writing
(give them all the rope to hang themselves with) and only then push back with all force in writing. Acas is a phone call away. I found them really helpful. You can threaten to take them to tribunal for breach of your stautory rights under equality act 2010.

https://www.peoplehr.com/en-gb/resources/blog/you-can-t-stop-employees-discussing-their-pay/

They might suddenly decide to drop all this as it is too much aggro. Got to also factor in the publicity angle when you would win at tribunal.

I work for the nhs and last year had to threaten tribunal via acas (you dont have to leave or resign first) due to breach of my statutory right. Head of hr relations was at my meeting. Hey presto, suddenly all apology, bending over backwards.....

I think what others have said is very helpful too. This informal warning, which policy does it sit under, does it even exist? If its not in writing, its not a policy and if all the people involved in the salary discussion have not also been threatened with this informal warning why have you been singled out?

I hope you can get this unpleasantness sorted out soon. Your manager must be a right sycophantic wimp not to have your back on this.

The manager who had to issue the letter confirmed that there is nothing in my contract or in any policy stating that we cannot discuss salary. He said it falls under "professional conduct", which I feel like is really subjective considering that I don't personally think that it is unprofessional.

Although it doesn't apply in the UK, point out the EU's Pay Transparency Directive to them, and ask them why it is acceptable in other European countries but considered unprofessional to discuss it in the UK.

https://www.cliffordchance.com/content/dam/cliffordchance/briefings/2024/11/the-eu-pay-transparency-directive-countdown-to-implementation.pdf

It is perfectly acceptable to tell people how much you earn.

Tell them to boil their heads (politely).