A federal judge in Texas hearing a lawsuit by 21 states over the Obama administration’s overtime rule, set to take effect Dec. 1, has declared the rule illegal and issued an injunction to block its implementation nationwide.

An Obama appointee, U.S. District Judge Amos Mazzant in Sherman, Texas, ruled that the Department of Labor (DOL) cannot establish overtime rules based solely on pay scales.

“If Congress intended the salary requirement to supplant the duties test, then Congress and not the department, should make that change,” he said. Duties tests consider an employee’s overall responsibilities to determine if a salary rather than hourly pay (plus overtime) is warranted.

The DOL and Obama administration can appeal the ruling, so employers may well choose to proceed as if the overtime rule will still take effect on Dec. 1. The injunction, if it stands, will serve as a bridge to a full court trial to weigh the merits of the lawsuit, both pro and con. The White House declined to comment immediately on the ruling.

In May, the DOL issued its long-awaited rule raising the bar on the salary threshold above which overtime pay need not be tendered, provided the employee meets other already-existing “duties tests,” from $23,660 a year  to $47,476 annually. The rule was set to take effect in a little more than a week from now.

Judge Mazzant declined to rule on the lawsuit’s claim that the DOL overtime rule violates the 10th Amendment to the Constitution, which delegates to the states all powers not granted specifically in the Constitution to Congress and/or the president.