The postponement creates space for Glencore to seek to secure the support of Qatar Holding, which wants a higher price for its 11 percent stake in Xstrata.
Qatar Holding's position is crucial to the hopes of other Xstrata shareholders who are demanding improved terms.
The delay on voting also buys time to gain regulatory approval to create the world's fourth-largest natural resources group.
The vote was originally set for Thursday. Glencore announced on Wednesday that it expected to hold its general meeting to approve the deal on Sept. 7 as well.
Qatar Holding, the government-backed investment fund, is holding out for a bigger price. Glencore is offering 2.8 shares for each Xstrata share, but the Qataris, who hold a stake of 11 percent, want 3.25 per share.
Other investors with much smaller stakes have also said they want more for their Xstrata shares.
Glencore shares were down 2.9 percent at 307 pence in afternoon trading in London; Xstrata shares were down 2.7 percent
The proposed all-share merger has gained regulatory approval in Australia, while the U.S. Department of Justice has taken no action during the waiting period after notice was given—an indication it will not oppose the move. But Xstrata noted that it is still in talks with the European Commission and that China and South Africa are reviewing the deal.
Glencore already holds a 34 percent stake in Xstrata but cannot vote its shares on the deal.
The deal, expected to be completed in the fourth quarter, will create a combined company to be called Glencore Xstrata with a market value of $90 billion. The company would control a chain of businesses from mining to refining, storage and shipping of basic commodities like coal, copper and corn.