Williams has had both cars disqualified from Singapore Grand Prix qualifying for a technical infringement.
Alex Albon and Carlos Sainz qualified a surprisingly muted 12th and 13th for Sunday's race at the Marina Bay circuit.
But they were referred to the stewards after their cars failed post-qualifying inspections.
When the DRS flap was checked, both cars exceeded the maximum limit of 85mm on both sides of the rear wing outer area.
Technical regulation breaches are usually a black-and-white matter, so it was no surprise that a double exclusion followed.
Williams said at the hearing that "their own measurement prior to the qualifying had shown the component to be within tolerance".
The team didn't contest the measurement and fully accepted the result, acknowledging its rear wings weren't compliant.
Team boss James Vowles said: "This is bitterly disappointing for the team and we are urgently investigating how this happened.
"At no point were we seeking a performance advantage and the rear wings had passed our own checks earlier in the day, but there is only one measurement that matters and we fully accept the FIA ruling.
"We have a car capable of scoring points here this weekend and will do everything we can to fight from the back of the grid tomorrow, and will immediately review our processes to make sure this doesn’t happen again."
It comes at the race immediately after Sainz scored his first podium for Williams in Azerbaijan.
Sainz had looked strong again through practice, ahead of Albon on pace and with a good chance of starting in the top 10.
But Williams struggled in Q1 and in Q2, and the failed post-race check escalates the team's disappointment further.
