A federal judge on Tuesday temporarily blocked what would be the biggest grocery store merger in U.S. history, siding with the Federal Trade Commission in its lawsuit seeking to halt the deal.

The preliminary injunction issued by Judge Adrienne Nelson sides with the federal regulators who have argued that Kroger’s $24.6 billion acquisition of Albertsons, a rival grocery chain, would risk reducing competition at the expense of consumers and workers.

Her ruling, which came about three months after a hearing that featurin testimony from top executives and economic experts, puts the merger on shaky ground as the companies defend their deal against two separate lawsuits filed in state courts.

This is a developing story. Check back for updates.