The Employers and Manufacturers Association has been found to have breached the Electoral Finance Act, and the case has been referred to police.
The Electoral Commission upheld a complaint about the association's advertisements criticising a law change.
Association chief executive Alasdair Thompson says the advertisements dealt with a plan to stop employers offering higher wages to workers who were not members of KiwiSaver.
Mr Thompson says the ads asked people to contact all political parties to voice their opposition.
He says it was never the association's intention to break the law, and that lobbying MPs on matters affecting companies was part of the association's core business.
Mr Thompson says stopping people from expressing what they need to say about issues before Parliament is "crazy" and the association will defend the case if police decide to prosecute.
