New York Times

WASHINGTON — In a pair ofSupreme Court arguments on Monday, about Internet shopping and railroads, the justices seemed unusually concerned that their answers to the technical issues before them could have vast ripple effects.

The case on Internet shopping concerned Colorado’s novel attempt to collect sales taxes on out-of-state purchases in response to the Supreme Court’s 1992 decision in Quill Corp. v. North Dakota. That decision said states may not collect taxes from companies without some local physical presence.

In 2010, Colorado tried a different approach, enacting a law that required out-of-state merchants to report transactions to their customers and to state tax authorities.

Justice Antonin Scalia wondered why the idea had not spread.

“Am I correct that Colorado is the only state that seeks to do this?” he asked Daniel D. Domenico, Colorado’s solicitor general. On hearing that it was, Justice Scalia said he found that “amazing.”

“The fact that it’s a one of a kind gives me some pause,” he said. “This is certainly a very important case because I have no doubt that if we come out agreeing with you, every one of the states is going to pass laws like this.”

The Colorado law was challenged by the Direct Marketing Association, a trade group, which said it violated the Constitution’s commerce clause. A federal trial court agreed, but the United States Court of Appeals for the Tenth Circuit, in Denver, ruled that the lower court had been without jurisdiction to hear the case.

A federal law, the Tax Injunction Act, requires that some tax cases be brought in state rather than federal court. The question for the justices on Monday was whether the case before them, Direct Marketing Association v. Brohl, No. 13-1032, was such a tax case.

George S. Isaacson, a lawyer for the trade group, said the federal law applied only to people and entities subject to taxes and not to bystanders who happened to have information relevant to tax collection.

Justice Elena Kag

an said she found the distinction unpersuasive. “Where do you get, Mr. Isaacson, this idea that the plaintiff has to be the taxpayer?” she asked. “Because certainly the text of the statute does not say that.”

Justice Stephen G. Breyer suggested that states could make residents pay sales taxes by requiring them to disclose out-of-state purchases on their tax returns. But he noted a possible flaw in his plan.

“If they tell you the truth,” he said. “This is the West. I understand. I’m from the West.”

In the railroad case, a trade group challenged a 2008 federal law that it said gave Amtrak, which carries passengers, too much power over freight railroad companies.

“The Constitution does not permit Congress to create a corporation, deem it nongovernmental, and then launch it into the commercial sphere with a for-profit mandate, and then vest it with regulatory authority over other companies in the same industry,” the group’s lawyer, Thomas H. Dupree Jr., said in describing Amtrak.

A lawyer for the federal government, Curtis E. Gannon, disputed almost every clause of that sentence. But there was no question that the 2008 law allowed Amtrak to play a role in setting performance standards.

Justice Anthony M. Kennedy said that was problematic.

“Suppose that the government together with auto manufacturer A made standards,” he said, drawing on a hypothetical example in a brief, “but then auto manufacturers B and C had to follow them. That seems wrong.”

But Justice Breyer said that some collaboration between industry and the government was both commonplace and valuable.

“I hope you will calm me down,” he told Mr. Gannon. “It seems to me there are hundreds, maybe thousands of organizations that set standards for the industry,” he said, mentioning the Internet Corporation for Assigned Names and Numbers, or Icann, which manages the Internet’s address system for the Commerce Department.

A ruling against Amtrak, Justice Breyer went on, could create “havoc, possibly with the Internet, possibly with industry throughout the United State

s.”

Mr. Gannon said that was possible. “I think it depends upon how broad the court’s ruling is,” he said.

But Mr. Dupree said there were important distinctions. “The violation here is that Congress has given Amtrak the pen” to write federal regulations, he said. As for Icann, he continued, “that’s not a situation where you have a company trying to regulate other competitors in the market.”

The United States Court of Appeals for the District of Columbia Circuitruled against the government on the ground that Congress had improperly delegated legislative authority to Amtrak. But at least some justices seemed more attracted to a second rationale for a ruling in the case, Department of Transportation v. Association of American Railroads, No. 13-1080.

“So long as it is operating on a for-profit basis and is given the last word on some regulatory matters that disadvantage its competitors,” Justice Scalia said, “there’s a violation of due process.”