To challenge this informal warning at work?

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).

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.

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.

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

Are the colleagues who were involved in any of the conversations also receiving written warnings? If not, why are you being singled out?

You don't need a rep at work.

You can contact them any time via email or a telephone number.

As a PP pointed out you couldn't consult them about this anyway as it's already happened.

But I'd join one ASAP for the future.

Absolutely agree with this. Full time officers I’ve come across at my union are great, and will represent at the more complicated cases (even though we do have reps in house, but as you say they are volunteers)

Ask for the following in writing:

The policy which provides for informal warnings and what happens with them. I’m public sector and we found out that these were being kept on record for 6 months (despite having no policy that allowed this). We’ve been challenging them since.

The policy which says you cannot discuss salary (these do exist in some companies but I think are quite unusual).

Full details of the complaint against you.

I would push hard here OP. I suspect they don’t have a leg to stand on.

Wow that's shocking.
I work in a vaguely similar field and got a pay rise through raising with management that a colleague told me what they were on. (They were doing the exact same thing and getting more) Neither of us got any warnings and it turns out they just genuinely didn't realize we were qualified to the same level.

Never knew it was a thing to not discuss pay with colleagues (other than it being a bit awkward!)

I can sort of understand it in a corporate sales type job but not healthcare, even private, because your qualifications and experience are quantifiable and jobs are pretty "set" in structure.

You can definitely join a union, like Unison. They won't support you immediately, but will in a few weeks.

Unison will still let you join in the private sector

i wouldn’t particularly challenge it but just say you had no idea you’d done anything wrong and can you see the policy they are referring to so you can avoid situations like this again

be very clear that you want to see the policy you have breached

You don’t say what you actually are employed as but if a nurse (you mentioned Band 6) could you not ask the Nursing and Midwifery Council or equivalent if it is appropriate and I suggest joining a union ASAP because your bosses sound a bit iffy. Good luck x

That's not necessarily a bad thing. My workplace didn't recognise a union, so there was no rep there - so I got one from the union who was employed full-time, rather than someone doing it as a voluntary thing, who might be excellent, but equally might not be at all

I don't think there is anything informal at all about a written warning. That's pretty much as formal as it gets. They don't want it on your record because then you might actually start to ask some tricky questions, like where's the policy and what's wrong with someone asking for fair pay. This is a way to threaten you without actually getting into the technicalities. I would also be making an extremely formal request to see the policy that you've never been made aware of in a written letter with a date and signature.

Not for a negative reason but because in some industries people are rewarded for soft skills that are hard to quantify, and those without them are likely unaware of their lack, so it's best if they never know.

That's some patronizing bullshit! "Don't tell her John's on more money because he's better at golfing with clients, it will only upset her". Rewarded for soft skills is one thing. Deliberately keeping it quiet is nonsense.

I do understand why in some workplaces it is counterproductive to discuss salary. Not for a negative reason but because in some industries people are rewarded for soft skills that are hard to quantify, and those without them are likely unaware of their lack, so it's best if they never know. But surely a quick chat could have addressed the issue, unless it is breaching a formal workplace policy in which case I suppose the letter is fair enough. If so I would just shrug and move on personally. At least you know you are being well paid OP!

@PaperwhiteTheGhost ACAS will give free impartial advice, so I suggest you contact them after you've asked where it is stated in the policy ( that you are not allowed to discuss salaries )

Why were you discussing pay? If it was because of a concern about equal pay issues, the Equality Act has an explicit section that makes any clause in a contract that forbids discussing pay unenforceable - although it only applies on equal pay issues. https://www.legislation.gov.uk/ukpga/2010/15/notes/division/3/5/3/14

So for example if you or a female colleague was concerned that a male colleague is being paid more than you, and you are trying to establish the truth, they cannot forbid you from talking about pay. If you are just having a gossip, you have less of a defence if it's forbidden in your contract.

So not really informal then.

The OP isn’t on a public sector salary.