While champions Mercedes are willing to agree, even if it erodes their advantage, the independent teams that pay the German manufacturer for engines appear opposed.
Force India deputy principal Bob Fernley said his team would resist anything that increased costs, while sources at Williams indicated it would make no sense for them to help rivals close the performance gap.
"I know it's on the agenda but I have no idea what the wording is. And more importantly I don't know what the cost implications are, because that will be the key to it," Fernley told Reuters at the Spanish Grand Prix on Friday.
He expected, however, that a fifth engine would cost an extra $1.5 million.
"That's why Williams wouldn't want it, why Lotus wouldn't want it and why we wouldn't want it," added the Briton, whose team have suffered cash-flow problems and have had to delay the introduction of upgrades.
Formula One allowed drivers five engines last year, the first of the new V6 turbo hybrid era, but the allocation was cut for 2015 with grid penalties for anyone exceeding the limit.
Force India and Williams are both on the key six team Strategy Group which also includes Mercedes, Renault-powered Red Bull, Ferrari and McLaren-Honda.
Fernley's team have already made their presence felt on the Group, in February scuppering a bid by the Manor Marussia team to be allowed to use last year's car.
After four races dogged by reliability issues, Red Bull's Australian Daniel Ricciardo is already on his fourth engine with 15 races remaining.
Russian Daniil Kvyat has also used three while Max Verstappen, at sister team Toro Rosso, is on his fourth too.
Red Bull principal Christian Horner said last month that he expected the allocation to be increased.
"For sure we are going to use more than four -- the chances of us staying within the limit of four is close to zero," he said in Bahrain last month.
"The teams agreed unanimously in Malaysia to introduce a fifth engine, but the engine penalties will affect others too, not only us...for us we would need that number to increase to seven, eight or nine engines for the season."
(Reporting by Alan Baldwin, editing by Nick Mulvenney)
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