As a physics graduate student at Carnegie Mellon University, Dacen Waters isn’t exactly living the high life. He earns about $28,000 a year working in a lab at the school — enough to live comfortably in Pittsburgh, a city with a relatively low cost of living, though not enough to have much left over after paying his bills.

But he says the Republican tax proposal could make things much worse. Now, he’s starting to worry he’ll get taxed on a paycheck he never sees. That’s because if the GOP’s Tax Cuts and Jobs Act becomes law, the $43,000 waiver he gets for his tuition at CMU would be counted as income for tax purposes.

“I still just scrape by as a graduate student,” said Waters, who is in the fourth-year of his program. “If this went through, I’m not financially stable enough where I could keep going.”

For many Ph.D. students like Waters, the tax-free tuition help is an essential part of the calculation that makes it possible to afford attending graduate school. It’s not uncommon for schools to lure students to Ph.D. programs with an offer to waive graduate students’ tuition in exchange for working as a teacher or in some other research function.

John Grisham: 'Day of reckoning' coming for student debt

Right now, for tax purposes, that money isn’t considered income. That preferential tax treatment is on the chopping block in the GOP tax plan and students are mobilizing. They are circulating documents estimating the potential tax liability for various students and holding a call your congressperson day Wednesday, among other efforts.

It’s that preferential tax status in large part that makes the model America uses for doctoral education feasible, said Ben Miller, the senior director for postsecondary education at the Center for American Progress, a left-leaning think tank. Since pursuing a Ph.D. is a long process, the only way most students can afford it is by having their tuition waived in exchange for some work.

“If you start to tax that tuition as income, you’re basically going to create a situation where students cant afford to get doctoral degrees,” Miller said. “They’re going to basically lose their stipend to pay taxes,” he added.

Put another way: “It’s just devastating to our community,” said Samantha Hernandez, the director of legislative affairs at the National Association of Graduate-Professional Students. The preferential tax treatment is so crucial to graduate students’ ability to make it through school that a similar proposal in the 1980s prompted the organization to form.

This year’s proposal comes at a time when some conservative higher education experts and policy makers are questioning the subsidies the government provides to graduate students. Republican Representative Virginia Foxx from North Carolina, the chairwoman of the House Committee on Education and the Workforce, hinted last year that she would curtail a federal lending program that allows graduate students to borrow up to the cost of their education. Foxx and others have said the program makes it too easy for students to borrow large sums they may struggle to repay and provides colleges with room to raise tuition on graduate programs.

The Trump administration’s Department of Education has also suggested changing income-driven repayment programs so they provide less of a benefit to graduate students. And officials have floated eliminating the Public Service Loan Forgiveness program, which critics say provides a boon to borrowers with advanced degrees, high incomes and high debt levels.

“There’s definitely a little bit of a class warfare element here,” Jason Delisle, a resident fellow at the American Enterprise Institute, a conservative think tank, said of Republicans’ interest in targeting subsidies to graduate students. “But there’s also a pretty strong fairness argument.”

Delisle noted that similar arrangements outside of academia, like technical apprenticeships, don’t get preferential tax treatment. “If you had a blue-collar job where someone is doing on-the-job training, that’s not tax-free income.”

But graduate students and even some professors argue that the preferential tax treatment benefits more than just the graduate students themselves. Without it, competitive Ph.D. students in science, technology, engineering and mathematics may choose to study in other countries — a major problem for U.S. universities looking to advance research in those fields and for American companies searching for talent.

“We need a lot of computer science Ph.D.s, we need engineering Ph.D.s and the tax code doesn’t distinguish by what time of program you went to,” Miller said.

What’s more, graduate students often serve core functions in the university community, Hernandez said. If their tax bill jumps to an unsustainable level, they may be unable to continue. What’s more, it could raise the cost of providing these people for universities, an increase they may pass on to undergraduates in the form of higher tuition, Miller said. “It’s completely ignoring an entire group in a higher education community and a very important group in the higher education community,” Hernandez said of the GOP’s tax proposal. “We teach the undergraduates.”