Fletcher Building has gone into a trading halt while it reviews the financial performance of one of its units after two profit downgrades this year.

The company told the stock exchange it is reviewing the financial performance of its Building + Interiors (B+I) business unit and the impact "on earnings guidance for the 2018 financial year".

KPMG is running the ruler over two of the largest projects in the B+I business and Fletcher said this was informing its review.

The trading halt should lift tomorrow, with the announcement of earnings guidance for the next financial year.

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The company also expects to announce the appointment of its new chief executive before the market opens tomorrow.

Former chief executive Mark Adamson left the company immediately in July as it announced a second earnings downgrade amid cost blowouts at two major construction projects - widely believed to be the Auckland convention centre and the Justice Precinct in Christchurch.

The company, at the time, also disclosed a $220m impairment against its Iplex Australia and Tradelink business units.

Meanwhile, up to 50 Fletcher Building workers will walk off the job today and more industrial action is to take place outside the building giant's annual general meeting tomorrow.

According to First Union, which represents the striking workers, about 50 workers had already walked off the job from Fletcher-owned companies Laminex, Mico, Humes and Firth Concrete.

Another 40 to 50 workers would be walking off today from Winstones Aggregates and the Hunua Quarry.

"The strikes will continue tomorrow where the workers - some coming from as far as Taupo - will be protesting the Fletcher's AGM at the War Memorial Museum in Auckland at 10:30am," a union spokesman said.

The workers would be joined by community activists protesting the Fletcher-led development at Ihumatao, bordering the historic Ōtuataua Stonefields.

Fletcher Building said that people unrelated to the company had been invited to participate in the demonstration.

"However we are expecting fewer than 45 people from three of our businesses to strike.

"Arrangements have been made to minimise any impact on our customers."