A group of big-business CEOs warned Tuesday that the economy could suffer if Congress and the Trump administration fail to enact tax reform this year or in early 2018.

"There's a big opportunity on the table here for the administration and Congress," said Joshua Bolten, the head of the Business Roundtable, an advocacy group comprising business leaders. "There's also a risk, because there's a real downside to the U.S. economy if they fail to get tax reform done in a timely fashion."

Bolten spoke to reporters Tuesday to discuss a new survey of the group's members, which found that they are very optimistic about the economy and have plans to increase hiring and investment.

But the idea that Republicans will succeed in passing tax reform is baked into those expectations, Bolten said. As a result, business executives might actually scale back plans for expanding and hiring if the tax plan goes down.

The vast majority of the CEOs believe the U.S. system of business taxation puts them at a disadvantage to companies overseas. When it comes to tax reform, they want to see the corporate tax rate lowest from the current 35 percent, which is the highest among developed nations. They also want to see an end to the unusual practice of taxing companies' foreign profits.

Those are among the very few principles that Republicans agree on. Otherwise, many specifics about the plan for tax legislation remain undecided.

Congressional Republican leaders have said that they plan to release a document with more specifics next week.