Although the agreement was designed in part to give smaller teams lower engine prices in the future, it's understood that the two teams feel that not enough help has been offered.

In addition, there are believed to be some questions about the process that led to the agreement being ratified.

As a follow-up, Force India deputy team principal Bob Fernley and Sauber boss Monisha Kaltenborn visited Ecclestone's motorhome in Barcelona last weekend, and the pair also met with Jean Todt.

Fernley confirmed that the two teams had written the letter, but he declined to elaborate on its content.

“A letter was sent to the FIA and the commercial rights holder, putting our position to them,” he told Motorsport.com. “I'm not going to deny that we sent it, but I'm not going to comment on it either.”

Meanwhile, the two teams remain involved in their joint complaint to the EU Competition Commission.

“The EU have slightly restructured because of the pressures that the competition department are under," Fernley explained.

"The sports complaints or enquiries have been put into one division. Because it's been moved, it has to go through process again - in other words, people have to get up to speed and so on. Once they are ready, they will advise us.

“From our point of view, we can only work with the process that's available to us, and obviously we'd like to see the EU investigating, because clearly we need an independent body that has the power to make changes if necessary, and should they feel our complaint reasonable.”

Regarding Ecclestone's take on the complaint, Fernley said: “In all fairness, Bernie has dealt with this in a professional manner. He knows we're not happy and he respects our position, and I think it's a case now of it just going through the process.”