Although the mailers did not identify who paid for them, the International Union of Operating Engineers Local 150 helped bankroll the campaign, Local 150 officials told WTTW News.

Advocates say the proposed ordinance aims to combat climate change and reduce the amount of greenhouse gas emissions, while critics believe it would increase cost and risk reliability.

There is a battle over a multi-billion dollar, decades-long project to upgrade Chicago’s aging natural gas pipelines.

The so-called “Workers’ Rights Amendment” aims to codify in the state constitution the right to form a union and collectively bargain over a host of issues. It would effectively prohibit any future anti-union legislation, like right-to-work laws.

The so-called Workers’ Rights Amendment would guarantee Illinois workers the constitutional right to collectively bargain for things like wages, hours and working conditions.