WASHINGTON (Reuters) - U.S. Supreme Court justices on Tuesday signaled skepticism toward a federal law that made it a felony to encourage illegal immigrants to come or stay in the United States as they heard a bid by President Donald Trump’s administration to revive the measure after it was struck down by a lower court.

Migrants, mainly from Central America and marching in a caravan, walk on a road on the outskirts of Ciudad Hidalgo, Chiapas, Mexico January 23, 2020. REUTERS/Andres Martinez Casares

The nine justices heard arguments in the administration’s appeal after the San Francisco-based 9th U.S. Circuit Court of Appeals in 2018 invalidated the law as a violation of the U.S. Constitution’s First Amendment guarantee of free speech.

Conservative and liberal justices alike expressed concern that the decades-old law may be too broad, repeatedly pressing the administration about what kind of speech could be criminalized.

Chief Justice John Roberts, a conservative, asked whether it would be illegal for a grandmother to tell a grandchild who was in the United States unlawfully, “I encourage you to stay.” Other justices wondered about the work of lawyers or charities and whether their speech could be impaired.

The law bars inducing or encouraging an illegal immigrant to “come to, enter or reside” in the United States, including for financial gain. The case involves Evelyn Sineneng-Smith, a U.S. citizen who ran an immigration consultancy in San Jose, California, and was convicted of violating the law.

It is one of a number of immigration-related appeals the Supreme Court is handling during its term that ends in June. The justices in November heard Trump’s bid to rescind a program that protects from deportation hundreds of thousands of young people known as “Dreamers” who were brought to the United States illegally as children.

Trump has made restricting both legal and illegal immigration a centerpiece of his presidency and his re-election bid this year.

Sineneng-Smith, convicted of violating this law as well as mail fraud, was sentenced to 18 months in prison and three years of supervised release. She was accused of profiting by duping illegal migrants into paying her to file frivolous visa applications while remaining in the country indefinitely. Her business primarily served Filipinos who worked as home healthcare providers.

The Trump administration said the law is not meant to criminalize protected speech, but rather to stop people who would facilitate or solicit illegal immigration and enrich themselves by doing so.

Liberal Justice Stephen Breyer wondered whether the law could be limited rather than struck down entirely. Some of his colleagues seemed to doubt its viability given the threat to even simple speech, pushing back against the administration’s attorney who suggested that a person urging a relative to stay in the United States would not be prosecuted under the law.

Liberal Justice Elena Kagan asked what would happen if the person gave 10 reasons to stay “and repeats that and repeats that, and it’s very definitely encouraging and inducing a person to stay in this country - does that count?”