What is the specific conduct you're considering? Have you received submissions from two students which Turnitin flagged as "at least 10% copied from other known work"? Are there inline citations and quotes which give sufficient credit for ideas and writing that the students didn't originate?

Turnitin is a tool to aid in detection of plagiarism, not a plagiarism oracle.

Not even citations are allowed? What? Does this mean that students are supposed to write papers on completely fictional made-up topics just so they can practice writing? Or are all students expected to lay the foundations of completely new fields of science? Otherwise there is no way to get around building your work upon the works of others. What field you are in? I wrote my thesis in an engineering field, and both me and all others basically took existing methods, and made improvements upon them, optimizing the general method for specific areas of application.

How can you improve existing methods without the ability to explain what they are?

"Including quotation marks and an inline citation does not get a student around this rule/instruction. I consider it to be plagiarism." ─ Why do you consider it to be plagiarism, if the student is not claiming the words or ideas they quote to be their own?

What is your core goal in disallowing explicit, acknowledged quotes of other work?

I see some votes to close this question. I urge people not to vote to close this question. It is disturbing that someone who does not at a very fundamental level understand what plagiarism is is teaching a class on how to write a scientific paper and enforcing this misunderstanding with potentially serious consequences for their students, but it's also commendable that they reached out for a second opinion, and the more answers this questions gathers, the more likely it is that the OP might change their mind and that their students won't have to face baseless accusations of plagiarism.

@vsz It's clear that what the OP means is that no verbatim quotations are allowed, not that the students are not allowed to cite any literature.

@AdamPřenosil I don't think it's clear -- look how many people asked for clarification in the comments. But I agree, I think that's what the OP meant.

I think the better-policy suggestions clarify why the OP has the rule they do: The total length and duplication ratio scores are automatic with tools like TurnItIn. If they need to count quotations separately, then that needs to be manually done and they don't have the manpower to do it. As a result, they have a rule that lets TurnItIn automatically lay down the law, and if TurnItIn flags a thing, they call it plagiarism. OP, is this correct?

I don't get all the fuzz. I teach engineering and disallow the use of formulas. It's very effective, students just have to guess the answer and everyone gets full points for creativity. Very easy grading, everyone happy.

On the other hand, the thesaurus enhanced quotes to get around the verbatim rule, might provide a bit of entertainment value in an otherwise thankless job of grading these essays ?

@leeman It may be hilarious, until you realize there are students learning how to write scientific papers by someone who doesn't understand some of the fundamentals they are teaching. Its scary to think of how many student's educations have been damaged having completed this course.

@DonQuiKong Solving engineering problems without formulas provides benefit, as you're still trying to solve a problem, but use alternative methods. Here, it would be like solving the engineering problems without the use of formulas written with numbers or symbols. But if you write out everything in words, its fine. And then the teacher is expecting the same results while calling anyone who wrote the answer with numerical symbol 7 a cheater but the student who wrote seven is fine.

@DavidS yes, that comparison is more correct. But less funny.