Incitec Pivot is facing challenges in prolonged discussions to sell its fertiliser division to Indonesian state-owned group Pupuk Kaltim.

The company is now contending with concerns from the Foreign Investment Review Board due to the sale's potential impact on Australia's critical phosphate supply.

Pupuk's non-binding offer has stalled due to proposed export caps and uncertainties regarding Incitec Pivot's gas supply agreements.

The fertiliser business is estimated to be valued at up to $1.5 billion.