The U.S. Supreme Court appeared interested in reaching a narrow ruling to avoid the consequences of blowing up the federal tax code in the blockbuster tax case of Moore v. U.S. as it heard oral arguments Tuesday.

The case, challenging a key element of the tax cuts signed by President Donald Trump in 2017, presents a novel tax question to the court. Could Congress impose a tax on U.S. shareholders unrealized gains (profits that are earned but not paid out, either as dividends or by other means) from foreign-controlled corporations?

While this matters for the tax at issue, the case was also seen as a stalking horse for preventing any passage of a wealth tax , like that promoted by Sen. Elizabeth Warren (D-Mass.).

Justices Brett Kavanaugh and Amy Coney Barrett appeared to be the most skeptical among the courts six conservatives of the argument put forward Tuesday by the plaintiffs lawyers. They could join the three liberal justices, who were not buying the plaintiffs arguments, to form a five-vote majority and rule narrowly to spare the tax (and reserve the question of the constitutionality of a wealth tax for a later date).

The case centers on the tax payments of a couple in Washington state, Charles and Kathy Moore. In 2006, Charles Moore, a former Microsoft software engineer, invested $40,000 in KisanKraft, an Indian corporation that sells farm equipment to small farmers, for an 11% stake in the company. The Moores profited from their investment but did not cash out those profits.

At the time, U.S. shareholders could defer tax payments on these kinds of profits earned by foreign companies until they were paid out as dividends. But in 2017, Republicans passed the Tax Cuts and Jobs Act, which included a Mandatory Repatriation Tax (MRT) that required U.S. shareholders, like the Moores, to pay a one-time tax on all undistributed income from foreign companies in which they held more than a 10% stake. And it was retroactive, applying to earnings after 1986. The total income believed to be held overseas in such corporations exceeded $2 trillion in 2015 and would generate $339 billion in tax revenue by 2027, according to the congressional Joint Committee on Taxation.