I'm a recent Ph.D. graduate looking for a postdoc opportunity in the US. I recently interviewed with my potential PI, and at the end he said we will discuss later. A week or two after the interview, the PI contacted my Ph.D. advisor for a reference. My advisor said that the PI had asked him for a online meeting. This was great at first, because it meant that he was interested in hiring me. However, what made me feel a little uncomfortable was that he never asked me for my Ph.D. advisor's contact information. I think it's natural to ask me first, as far as my way of communication is concerned. I would've been happy to give him my Ph.D. advisor's contact information. He and my advisor eventually had an online meeting in a positive atmosphere. My advisor says that he seems to be very interested in hiring me, and my advisor also said good things about me. Anyway I wonder if this is a red flag for the PI's communication style or personality. It the first time for me being at a academic job market in the US (and I'm not the one from english-speaking culture), so maybe I'm being too sensitive and reading too much into it. What do you think about this?
No, it's not a red flag at all, you are overthinking it.
While on the face of it the situation looks a bit like back-channel reference solicitation, which if frowned upon, I think this situation is different. It is universally assumed that while looking for your first postdoc job, your advisor will be your main reference. So functionally, all they did is cut some social dancing for the sake of efficiency. Consider that it's quite likely that they have met or corresponded before; this would make them asking you for contact details even more artificial.
In my experience this is not uncommon. (Although I guess the uncommon element is that you were not asked for a list of (potential) references when you applied, or did not give your advisor as a reference when asked.)
Asking colleagues about their opinions about on potential hires is fairly common practice. Usually this involves people the potential PI knows well, and whose judgement they trust, which could include the (former) supervisor.
Depending on the jurisdiction there may be some rules that need to be taken into account. For example, the fact that you applied somewhere, can be protected private information, that the potential employer isn't free to share. Similarly, there might information about the applicant that the supervisor isn't (legally) allowed to share. But, many of these can be skirted around by staying vague on the reasons why the exchange about the applicant is being held.
I wouldn't say that any if this is a red flag, per se. It tells you something about the potential employer. In particular, that they are probalby not the type to follow strict protocol, but that might not be a bad thing, depending on your own inclinations.
It is 50% of a red flag.
Some PhD students have advisors who behave badly or unreasonably. Others might have all kinds of other reasons for not wanting their advisors to be approached like this. For example they have told their advisor something about where they are looking for jobs, or they have not told them certain things.
The potential PI should have asked you first before contacting your advisor, and this incident suggests that the potential PI is somewhat inconsiderate.
I don't agree with Kostya_I who says "all they did is cut some social dancing for the sake of efficiency."
For me it’s 50/50 red flag. If you have officially provided list of references, then your potential postdoc PI should be contacting them first. If you haven’t provided contact details of your major advisor, then contacting with your major advisor without letting you know may reflect your potential post-doc supervisor’s style of management. Some people may like it, but I personally don’t think that good. It could potentially be harmful if you don’t have good relationship with your major advisor—-common in PhD level. Your PI should have at-least asked you why you haven’t provided your major advisor’s contact details and if it is okay to contact your advisor.
There are some things to take into consideration. If you applied to be my postdoc for example, then I need to secure about $115,000/year just to pay your salary (you probably only see 55-70k depending on location, but overhead, health insurance, everything else adds up on my end). That is a sizeable chunk of change from a grant - thus a big investment to just go in blind.
I will almost as a default assume your main reference will be your advisor. They know you and your research habits, and your ability to integrate and contribute to a group better than anyone else. If they are not, that is a MAJOR red flag. It will prompt me to investigate.
So, I will be inclined to reach out to your advisor, people I may know at your institution etc. Perhaps I may even know your advisor from some professional interactions.
Most faculty are well aware that advisor-advisee relationships do not always work out, especially at the interpersonal level. We take advice and comments with a grain of salt and we weigh them against your other references and your CV. For the most part, unless you have created serious issues in that group (delinquent, abrasive or confrontational, etc...) most people will find something positive to say about their former students... because ultimately you getting into a good postdoc reflects well on them in the long run. So unless you are trying to hide something serious, it's rarely an issue that would impact you (in my experience).
Not a red flag. If I am looking to have someone join my group, get paid off my grant, etc., I have to do my due diligence and I am not going to ask permission to do it. The PhD advisor is the first person I want to talk to. Now, there may be certain circumstances wherein I wouldn't necessarily take everything they say at face value, but I'm sill going to hear what they have to say. (I see others have written essentially the same thing).