Executives at the commodities firms were already seeking to rejig pay packages linked to the tie-up when the Qatar Investment Authority broke cover to seek a better deal for its 11 per cent stake in Xstrata.
The sovereign wealth fund, which was previously thought to be supportive of the deal, said it wants 3.25 new Glencore shares for every one existing Xstrata share, compared to the current ratio of 2.8 shares.
Both firms have seen their stock tumble since the tie-up was announced in February, eroding the value of the deal for investors.
Qatar said it still sees merit in the planned merger, but would like to see a “more appropriate distribution of benefits”.
Other stakeholders, including Standard Life, Schroders and the Association of British Insurers, have hit out at the generous bonuses on offer for top staff who stay with the enlarged company post-merger.
“Shareholders have been vocal ... and there is also a silent majority. We are all working to get the right outcome,” said one source familiar with the negotiations.