New Zealand's Commerce Commission filed proceedings with the Auckland High Court against Fletcher Building's (NZE:FBU, ASX:FBU) plasterboard subsidiary Winstone Wallboards, according to a Friday statement from the regulator.

The regulator alleges that the subsidiary's historical use of retroactive tiered rebates in supply deals with sellers between 2017 and 2022 breached the Commerce Act.

"While the use of rebates can deliver benefits, retroactive tiered rebates can also harm competition when [they are] used by a supplier with substantial market power because they can reduce the ability of smaller suppliers or new entrants to compete," said Commission Chair John Small.

In a Friday filing with the New Zealand and Australian bourses, Fletcher Building said that it has been made aware of the regulator's intention to file a case since Aug. 23 and that Winston Wallboards will "vigorously defend" its position before the high court.

Fletcher Building's shares were up almost 1% in recent Friday trade in New Zealand.

Price (AUD): $3.02, Change: $+0.02, Percent Change: +0.67%