"Can" they do it? Most likely yes (unless you have a written contract that says that you will be financed exclusively through RA positions, which is unlikely given your usage of the word "promised"). Is it underhanded? Also yes. These things are not mutually exclusive.

@xLeitix I am not the student in question so I don't know exactly what they have but the RA was in the offer letter. The exact wording and fine-print is not something I have access to.

It might be possible to negotiate an additional semester of research assistantship beyond the end of the initially promised period to "make up" for the TA time. Of course, the value of an RA position early in one's doctorate is different than its value later in one's doctorate, so it's not strictly a like-for-like exchange; but it seems like a reasonable request to make.

"as well" or "instead"?

@Azor "as well." As I understand it, the RA is not going away but they also have to teach. I am not sure how that works with the original RA being 50%. It must have been scaled back to 25% RA and 25% TA but i don't know for sure. Scaling back the RA seems like it would be off-sides.

What does "off-sides" mean here?

@Azor By "off-sides," I mean "against the rules." It seems to be that if a student is promised a 50% research assistantship but then gets a 25% RA and a 25% TA, that would be somehow illegal rather than just underhanded.

Probably the exact language of the contract matters. I would be very surprised if the department didn't give themselves an out. Toxic behavior, but my guess is it will end up being legal ... :(

In addition, a few US schools now have graduate student unions; if your school has one, it would be worth checking with them about what recourse might be available.

@aquaticapetheory I would also entertain the possibility that you or your friend are making a mountain out of a molehill. The grad student union presumably consists of more experienced students that have seen the different funding models play out in practice. If they don't consider this change a big deal, I am inclined to believe that it probably isn't.

Business needs changed, so the way support for a student is provided change as well.

@xLeitix This is not a mountain out of a molehill. If the promise was actually made, a promise to RA and not TA for "some number of years" (suggesting 3+) is a big deal; and taking that away the first semester is hugely inappropriate, in the same way someone getting hired for a 100% remote job being told they're now expected to be 50% in-person would be.

Can you clarify if the offer was for a set number of years of RA support or was it for RA support during the first n years?

@Terry It was RA for (i think) 3 years. My impression was that it was of the form "we offer you a 50% research assistantship for the first 3 years" but i'm not 100% certain of the actual numbers. After that initial period, the student will have to find funding.

So a 100% TA this semester and 100% RA next semester fits the offer (not even counting summer support)...

@Jon I assume you mean 100% of 50%. I would not consider that equivalent since the student has a PI that they are doing research for and the research work is not being put on hold for semesters with TA duty. But this is moot because the TA assignment started in the fall semester and is continuing in the spring semester. This is already at least 1/3 of the promised RA-only period where the bait was switched.

@JonCuster Surely you know that appointments are usually expressed in FTE equivalents, where 50% is the usual appointment. Obviously aquaticape isn't quoting the exact text but don't intentionally misread things it's not very helpful.

After re-reading your question, I think we need slightly more information. Is the TA requirement in addition to the RA, or in place of (a portion of)?

FWIW, in my experience doing a TA-ship can be a degree requirement, independent of whether or not the student has an RA or other funding.

@aquaticapetheory It's kind of a problem that you're asking here as a third-party, because that means there's necessary information that you don't have.

To me, it seems quite unreasonable to take promised RA years and make them TA years, but if the students will still get 3 years of RA, and the TAship is added on during the first three years, that doesn't necessarily seem like something worth complaining about

If the degree is expected to take 5 years, and students need to find funding arrangements for the second two years, having some of those students TA in their 2nd year to get an RA in the 4th year might be a perfectly reasonable trade. Of course it would be better to approach the students with this fair trade offer rather than a decree that they are now TAs, but it's not clear what the actual situation is if you don't have that information to share

@Neal I don't believe it is a requirement. I think the student chose this program over another because the other had a requirement for some TA time. This school may have some fine-print that says "you may be required to TA" but don't publicize it.

@Bryan Yes, it is vague and hypothetical since I am asking about someone else's situation. The best I expect here is "if this is the situation it's BS and action can be taken but otherwise they're out of luck." My impression is that the RA is for the first 2 (or 3) years and the new TA duty does not displace the original RA into later years. I also don't know if the original 50% RA is scaled down so that 25% TA can be added or if the student is being payed for 75% work but I doubt it.

@aquaticapetheory Sure, but if the situation can range from 'they're getting completely screwed' to 'it's really not a big deal' depending on those details the answer swings completely from one end to the other, too

@aquaticapetheory, I should clarify that I don't think it's common. In fact my only experience of this was that it happened to me. I had an external fellowship paying a stipend and my tuition, but the grad advisor told me I had to TA anyway (just once, though) justifying this by saying it was a degree requirement. I was a bit surprised but went ahead and did it. IIRC, I didn't check carefully that it was actually a documented degree requirement.

I don't recall whether I was paid.

@BryanKrause @Bryan I realize that. I will likely find out more detail at some point and hope to be better equipped to understand the situation given the feedback here.