The city’s Department of Investigation commissioner said on Thursday that he put gas company National Grid “on notice” following the arrests of several former employees accused of installing illegal gas meters across Brooklyn.

More than three dozen people, including seven National Grid employees, were indicted on Thursday, accused of installing the meters at 33 different residences throughout the borough, including in Williamsburg, Bedford-Stuyvesant, and Brooklyn Heights, as well as in parts of Queens, according to the Brooklyn District Attorney’s office.

The illegal orders would then go through the gas company’s main Brooklyn offices, according to the DA’s office.

“National Grid did not have sufficient internal controls in place to prevent this,” DOI Commissioner Mark G. Peters said. “And if you are running a large utility with something as dangerous as gas, you really ought to have sufficient internal controls in place to make sure this doesn’t happen.”

The entire enterprise was allegedly run by Weldon “Al” Findlay, 47, who is accused of coordinating with landlords to install the meters, avoiding possible months of red tape for required tests. Findlay, who worked for the gas company until 2010, would then ask how many meters they needed and text back a price, usually around $1,500 per meter, according to the DA’s office.

Peters said multiple violations were found when the buildings involved were inspected following the investigation, including the use of “cheap, plastic flex” hoses, which was one of things found following the gas explosion on Second Avenue in 2015.

Findlay is charged with enterprise corruption. If convicted, he faces up to 25 years in prison. Findlay was held in lieu of a $750,000 bond, according to the DA’s office.

A total of 37 defendants were charged following the investigation, which ran from Jan. 12 to June 30, 2016.

“This corruption within a major company is particularly alarming given the potential lethal nature and consequences of unsafe gas instillations,” acting Brooklyn District Attorney Eric Gonzalez said.

A representative for National Grid said the company is conducting an internal investigation and will work with the New York Public Service Commission, who regulates gas companies.

“National Grid has zero tolerance for unethical and illegal behavior,” the spokeswoman said in an email. “National Grid has fully cooperated with and has supported the Kings County District Attorney’s Office and the NYC Department of Investigation throughout their investigation, has conducted safety inspections, and has taken corrective measures where needed.”