A row over the ownership ratio in the mooted merger between EADS and BAE Systems is the latest threat to a proposal which would create the world's biggest aerospace group.
Sources said on Tuesday a 60-40 split in favour of EADS was being questioned on several sides and talks were under way about possibly adjusting it. Both companies issued denials.
Europe's biggest defence deal in a decade faces several hurdles including how to ring-fence top secret projects and how to satisfy governments keen to safeguard EADS operations in France and Germany.
With an October 10 deadline to decide whether the talks proceed, EADS chief executive Tom Enders, one of the merger's main architects, faces the German parliament on Wednesday to put forward his case.
Yet two sources familiar with the transaction said the deal, which the firms acknowledged publicly on September 12, already faced differences on how the two would be valued.
They said EADS and BAE were discussing valuing EADS at more than the 60 percent originally announced, pushing the ratio to potentially 63:37 or even 65:35.
"The ratio could be changed up to 3 percentage points in favour of EADS," one EADS adviser said.
EADS and BAE issued a denial: "The joint announcement published on 12 September outlining the 60-40 shareholder split is the only valid statement on this subject".
It said "any speculation suggesting a different ratio is inaccurate".
Some investors have argued the proposed ratio is weighted too heavily in favour of BAE, which is heavily exposed to shrinking military budgets.
BAE is Europe's largest defence company and a top 10 supplier to the United States, by far the largest defence market.
GERMAN GOVERNMENT EYES 70:30
Germany's Daimler, which was in talks to sell a 7.5 percent stake in EADS to Germany's state bank KfW, is one investor unhappy with the terms.
The German government on Monday set out a list of reservations about the deal, saying a 70:30 ratio would be a more accurate valuation, yet other sources familiar with the talks said BAE would likely oppose such changes.
"Changing the 60/40 split is just not on the table at all," said a banker working on the deal, who declined to be named.
Rationale for the merger includes striking a balance between civil and military revenues, with Airbus airliners on one side, and on the other BAE's defence work, which ranges from nuclear submarines to armoured personnel carriers.
Yet the deal is fraught with national economic and security concerns. A mooted merger between operations on the two sides more than a decade ago collapsed.
The French government holds a direct stake in EADS and is concerned that the deal would dilute its influence, while Germany wants to keep jobs in the country.
German Chancellor Angela Merkel met French President Francois Hollande to discuss the plans at the weekend, but they failed to come up with any joint decisions.
Gravity always wins!