UPDATED Jan. 21, 2015

President Barack Obama is proposing a major change to 529 college-savings plans—removing a tax benefit that has attracted parents to these investment vehicles for years.

Talking points for the president’s State of the Union address Tuesday night, released by the White House over the weekend, include a long list of proposed tax changes. Among them: no longer allowing earnings on new contributions in 529 plans to be withdrawn tax-free.

If that became law, it would be a major revision to 529 plans, and plan experts say such a change would likely result in contributions to these plans declining substantially. “Contributions would dry up in 529 plans,” says Joe Hurley, founder of Savingforcollege.com, which tracks 529 plans. Over time, as families withdraw the dollars they have stashed in these plans in order to pay college bills, he says the plans might “have a difficult time even staying in existence.”

He speculated that the president’s proposal might spur parents and grandparents to pump a lot more cash into the plans in advance of possible changes.