NGK Spark Plug says it has concluded a plea agreement with the US Department of Justice (DOJ), agreeing to pay a fine of US$52.1m based on charges that it violated antitrust laws in connection with sales of automotive spark plugs and oxygen sensors.

Since July 2011, NTK group says it has cooperated fully with the investigation. As a result of comprehensive consideration of applicable law, factual investigation and various circumstances, NTK has decided to enter into a plea agreement with the DOJ.

The impact on the company's financial forecast for the second quarter and full year of ending March 2015 is currently being reviewed, and NTK says it will disclose it as soon as any amendment is needed.

NTK also said that it has been consolidating its compliance systems. Since learning of this investigation, NTK has "strived to further enhance and review its compliance systems, including in-house training for antitrust laws and any other applicable laws, to prevent a recurrence".

In addition, NTK said that "to emphasise the seriousness of these matters", NTK's representative directors will voluntarily return 30% of their compensation for a three-month period starting from September.

The company also said it has apologised to all its customers and other stakeholders for any inconvenience or concern.