Commission files proceedings against Winstone Wallboards

The Commerce Commission filed civil proceedings against Winstone Wallboards Limited in the Auckland High Court on 1 November 2024. The proceedings follow an investigation opened in late 2022 into the company’s historical conduct in the manufacture and supply of GIB‑branded plasterboard between 2017 and 2022.

The Commission alleges that Winstone Wallboards, a subsidiary of Fletcher Building, breached sections 27 and 36 of the Commerce Act 1986. The allegations centre on Winstone’s use of retroactive tiered rebates in supply agreements with building‑supply merchants. Under these arrangements, merchants received discounts across their entire purchase volume only if they met specified targets. The Commission contends that this structure harmed competition by discouraging merchants from purchasing even small volumes from rival plasterboard suppliers, thereby limiting the ability of smaller competitors or new entrants to gain market share.

Fletcher Building has stated that Winstone Wallboards intends to vigorously defend the proceedings. The company argues that volume‑based rebates are a standard commercial practice in the building industry and notes that the Commission previously investigated similar conduct in 2014 but did not take enforcement action at that time.  Fletcher Building also acknowledges that Winstone Wallboards moved to a flat pricing model in 2022, although the Commission is seeking declarations and civil pecuniary penalties for the historical conduct.

The Commission’s concerns about retroactive rebates align with findings from its 2022 Residential Building Supplies Market Study, which identified such rebate structures as a potential barrier to competition.

As at April 2026, the case remains before the High Court and no trial date has been publicly announced.