Could be harmless, could be bad.
It's clearly significant:
Written invitation and HR presence means it's something official where HR makes sure that all laws and procedures are followed.
Most likely a formal change to your work arrangements.
How to prepare: Keep your eyes and ears open.
Are there any financial troubles, reorganizations, layoffs, acquisition, etc.
happening?
Make sure you are up to date on the state of the company and the business Be prepared to listen a lot and say little.
Politely nodding your head, mumbling "I see".
Don't say "yes" or "no".
Ask questions, especially if you don't 100% understand what they are saying.
"Can you clarify?".
"What does that mean specifically", "What are options for the next step", etc.
Your boss and HR have a huge information advantage, so your main goal is to learn what is there to be learned and buy some time to digest the information and formulate your own strategy how to deal with this.
DON'T SIGN ANYTHING in the meeting.
If they give you papers, ask for time to thoroughly read through them.
Prepare for the worst.
This could be a termination meeting.
Make sure that, if push comes to shove, you can leave the same day on short notice.
Clear up personal files and e-mail accounts from work computers.
Clear sign in credentials from browser caches, make sure your personal stuff is ready to go.
Don't stress too much.
It could also be something good.
Preparation is good, but only if it's constructive.
Worrying without doing just makes you more nervous.
workplace.stackexchange.com/users/5418/Hilmar
Is your company a union company?
If so, check if you have a right to bring a union representative the same way that your boss has someone from HR.
Most likely, you do.
Because the one thing you want to avoid is being in a 2 vs. 1 situation that could turn into a "he said /
she said" conflict.
Announce this before, and treat it as a perfectly normal thing.
If pressed, explain calmly that since you don't know what the meeting is about, you are sure that the presence of the union rep is entirely unnecessary, but you brought him just in case, so no time is lost in fetching him if his presence should turn out to be of advantage.
That doesn't mean this is bad.
It really could be entirely harmless, and the HR person might be there not to check on you, but to check on your boss.
But the point is that you don't know .
So better safe than sorry.
If you don't have a union rep on hand, then @Hilmar wrote a very good answer on how to prepare and behave, especially points #2 and #3.
workplace.stackexchange.com/users/71721/Tom
I would like to press that HR is not your friend.
Whenever HR is included that means change is coming (good or bad).
Unlike other answers, I think that if it's something good, your boss will give you a heads up while waiting for HR's confirmation.
I highly suggest preparing No.4 from
@Hilmar's answer : Prepare for the worst.
This could be a termination meeting.
Make sure that, if push comes to shove, you can leave the same day on short notice.
Clear up personal files and e-mail accounts from work computers.
Clear sign in credentials from browser caches, make sure your personal stuff is ready to go.
workplace.stackexchange.com/users/43137/clueless007
Besides @Himlar 's valuable gems, I would like to add the following based on my bad times with biased HR: If anything is going seriously against you, put your disagreement on record in the written form.
If they talk about any damages to the organization, even if you are lured to accept it by indirect indication that they will forgive if you accept, don't get lured.
It is a well known trap.
They may try to provoke you by direct/indirect insults and get something on which disciplinary actions could be taken.
Keep your calm until the meeting is finished.
Keep us posted after the meeting is over.
What it was about and how you handled it.
workplace.stackexchange.com/users/98316/Rajesh Kakkad
Do you have any reason to believe that it is not exactly what your manager said?
One-on-one could easily be boilerplate in the letter basically saying the meeting is just for you and not your whole team or department.
Have you signed a new contract with a shift change as your manager indicated?
If I had a contract change, especially with a shift change, with my current employer, this is exactly what I would expect to happen.
HR is more qualified to discuss contract language than your boss.
Since this is a change to your conditions of employment, HR should be present, just like they probably were on your first day of work/orientation.
workplace.stackexchange.com/users/3345/cdkMoose
I have received a letter from my boss saying that a meeting has been arranged for this date and time, and a member of HR will be there.  That is all the letter said.  When I asked the boss what the meeting was about she explained that it is a one-on-one meeting to discuss the contract I signed and talk about the shift change. I'm confused as to why a member of HR is attending on a supposedly one-on-one meeting and no other explanation was given.  How should I prepare for this meeting?
Meeting with the boss one-on-one but a member of HR will be attending
workplace.stackexchange.com
<human-resources><united-kingdom><meetings>
workplace.stackexchange.com/questions/126925
workplace.stackexchange.com/users/98307/David
Keep calm and listen carefully. Be prepared to be asked to leave on short notice. Make sure your computer is clear of personal files and passwords. Without knowing exactly what the meeting is about, the most important thing will be to listen and pay close attention both before and during the meeting. However, you will want to prepare for the worst, just in case, and this means both mentally and physically. You may want to make sure that your belongs are ready to go should you have to leave. But despite this potential risk, you should aim to stay calm and not stress too much, including during the meeting.
You should be prepared to listen and pay close attention. You may want to make sure that all of your things are ready to go should this turn out to be bad news. Be mentally and physically prepared for the worst possible news. Try not to get too stressed, and stay calm throughout the meeting.