Liberal Justice Ketanji Brown Jackson issued her first solo dissent in a Supreme Court merits case on Thursday, disagreeing with her colleagues in a labor dispute ruling that makes it easier for companies to sue over worker strikes.

In an 8-1 decision, the high court overturned a lower ruling that found federal union laws preempted concrete company Glacier Northwest from bringing its lawsuit against the International Brotherhood of Teamsters, which represents the company’s truck drivers.

Jackson wrote that the courts had “no business delving into this particular labor dispute at this time.”

“[T]he majority also misapplies the Board’s cases in a manner that threatens to impede both the Board’s uniform development of labor law and erode the right to strike,” Jackson dissented.

The case arose after the union directed its drivers to go on strike on a morning it knew the company was mixing concrete, loading it onto trucks and making deliveries. The concrete mixed that day was ruined, and Glacier sued the union for damages in state court.

Under a 1959 Supreme Court precedent, San Diego Building Trades Council v. Garmon, the National Labor Relations Act (NLRA), a federal law that governs strikes and collective bargaining, preempts state law when the two arguably conflict.

After the union got the lawsuit tossed at the Washington Supreme Court under Garmon, Glacier Northwest appealed to the nation’s highest court.

In a majority opinion authored by conservative Justice Amy Coney Barrett and joined by four of her colleagues, the court ruled that the NLRA did not preempt the lawsuit, because the strike did not take reasonable precautions to protect the company’s property from foreseeable, imminent danger.

“The Union’s actions not only resulted in the destruction of all the concrete Glacier had prepared that day; they also posed a risk of foreseeable, aggravated, and imminent harm to Glacier’s trucks. Because the Union took affirmative steps to endanger Glacier’s property rather than reasonable precautions to mitigate that risk, the NLRA does not arguably protect its conduct,” Barrett wrote.

Three additional conservative justices — Justices Samuel Alito, Clarence Thomas and Neil Gorsuch — wrote separately to reverse the union’s win on other grounds.

Jackson, on the other hand, stood alone in dissenting, marking her first solo dissent in a merits case since joining the bench last year. Jackson has, however, dissented solo outside of the court’s normal docket.

She noted a complaint submitted after the state Supreme Court’s ruling by the National Labor Relations Board’s general counsel, which alleged Glacier Northwest engaged in unfair labor practices in relation to the strike.

The majority found that “this issue is not properly before us” because the lower courts had not addressed the significance of the complaint, leaving it for the state courts to consider as the case proceeds.

“The filing of the General Counsel’s administrative complaint necessarily suffices to establish that the Union’s strike conduct is ‘arguably protected’ within the meaning of Garmon. Thus, the General Counsel’s complaint should have marked the end of any court involvement in this matter,” Jackson wrote.