Supreme Court justices struggled Tuesday to interpret whistleblower provisions of a federal law in a way that would protect some private company employees who do work for public companies, but not all—not, for example, the gardener who mows the company’s lawn.

Business groups say the outcome of the case Lawson v. FMR could mean the difference between protection under the Sarbanes-Oxley Act for whistleblowers at 4,000 publicly traded companies versus the same protection for workers at as many as eight million private firms that may have dealings with public companies.