GROWER economic interest and the way CCS is calculated are two remaining flies in the ointment of a marketing deal between Queensland Sugar Limited and Wilmar Sugar.

The forward progress of negotiations and the roll out of grower pricing agreements last Friday were described as an "important milestone” by QSL CEO Greg Beashel.

However smooth negotiation hit a wall on Tuesday after QSL discovered Wilmar's terms included re-defining the grower economic interest, which would mean less sugar for QSL to sell at the beginning of the season.

QSL say this would mean lower advance payments for growers.

"We strongly refute Wilmar's claim that this position was consistently in documents provided since October 2016. It has never been the subject of any of the negotiations between QSL,” Mr Beashel said.

Wilmar's executive general manager in North Queensland, John Pratt, announced further mediation to be facilitated by Richard Chesterman QC on Tuesday.

"We are keen to clear this obstacle as quickly as possible,” he said.

Mr Chesterman was the Queen's Councillor who brokered the "in principle agreement” between the warring parties in March.

Mr Beashel said on the table, when mediation begins tomorrow, is the issue of actual commercial cane sugar (CCS) versus relative CCS.

A point the Wilmar boss refuted.

"I want to quash any suggestion that Wilmar is moving away from using CCS relativity in the calculation of grower payments for cane and GEI Sugar. We have no such plan,” Mr Pratt said.

With the 2017 crush only four weeks away for some Wilmar mills the pressure is on to agree on terms which have had the two parties at loggerheads since the Queensland Parliament bought amendments to the Sugar Act in December 2015.