A U.S. judge grilled a Justice Department lawyer on Wednesday over deals President Donald Trump has reached with nine large law firms as she weighs the constitutionality of an executive order targeting the Perkins Coie law firm.

On March 27, Trump ordered the federal government to stop working with Wilmer Cutler Pickering Hale and Dorr LLP (WilmerHale)—suspending the law firm’s security clearances, directing federal agencies to terminate contracts they have with the firm, and limiting WilmerHale employees’ access to government buildings.

The blocked portion of the order would have changed the federal voter registration form to indicate proof of citizenship is required.