Fourteen people have been arrested during dawn raids in a number of cities as part of an investigation into a suspected multimillion-pound landfill tax fraud.
Around 180 officers from HM Revenue and Customs (HMRC) and local police officers descended on properties across the North East and Yorkshire.
The investigation, which is looking at a suspected £78m fraud, targeted six commercial and eight residential addresses in Gateshead, Washington, Hartlepool, Middlesbrough, Leeds and Hull.
Simon York, director at the HMRC fraud investigation service, said: "Today's activities are the culmination of 18 months painstaking investigation into the suspected systematic abuse of the landfill tax system.
"We believe that over £78 million revenue may be involved, money which could be used to fund some of the UK's most vital public services.
"No one is above paying their fair and legal share of tax, as the rest of us do, and we are closing in on those who try to cheat the system.
"HMRC, working with our law enforcement partners, will do everything within our power to catch those involved in tax fraud of any kind, and will push for the strongest punishments through the court."
In total 11 men and three women were arrested, ranging from 23 to 49-years-old.
A spokesman for the Environment Agency said: "The Environment Agency is supporting HMRC in a major operation at locations across Yorkshire and the North East.
"We are working closely with our partner organisations to help stamp out landfill tax evasion."