The dispute over bonuses at Kilmarnock intensified last night with the players' union insisting the club has imposed the lowest rate in the Premiership.

Officials at PFA Scotland have been called in by their members at the Ayrshire club over the package set up by Michael Johnston, chairman of the board.

It is understood Kilmarnock has ended its policy of paying league win bonuses throughout the season. Instead, the club will impose a sum that is split at the end of the season.

However, Fraser Wishart, the chief executive of PFA Scotland, told STV last night his members wanted the same system that applies at other clubs in the division. This is understood to include bonuses throughout the season and a final payment based on league position and appearances made by individual players.

Speaking to STV, Johnston said: "We had a good discussion and we gave an explanation of why we've offered what we've offered. Under UEFA guidelines clubs must ensure that their wages- to-turnover ratio does not exceed 70%. There is little wriggle room due to current financial expenditure on players' wages. We are trying to make income match expenditure and operate within UEFA regulations. We haven't finished the discussions."

However, Wishart said the club had not responded to the counter offer by the players. He said: "As a union we encourage all of our members to discuss and agree bonus schedules early on with their clubs; this is best practice and an agreement in writing will prevent issues arising later in the season for both parties. The Kilmarnock players did this on day one of pre-season. In this case, the bonus schedule was simply presented to the players and was far lower than any of its competitors.

"The players made a perfectly reasonable counter proposal, and although it would be entirely inappropriate to go into detail of confidential discussions, all the players at Kilmarnock are looking for is a bonus structure at the club which simply brings it into line with comparable clubs. As yet the players have not had a response to their proposal and as always are happy to discuss this matter further."

Johnston said: "There was a counter proposal. The club then requested the players' union produce evidence of what other clubs were offering [in] bonus payments. No such evidence has been forthcoming from Fraser Wishart."