The FIA will not include driver salaries or marketing costs in its proposed £30m budget cap, scheduled to be introduced next season.

In a letter to the teams, Max Mosley warns that without the budget cap option at least two of the current F1 teams could follow Honda's example and leave the sport. Consequently, ahead of next week's meeting of the world Motor Sport Council when he plans to unveil the full package, Mosley has given the teams until close of business today to inform him of any revisions they feel should be made.

"We are now close to concluding the regulations, both financial and technical, for presentation to the World Motor Sport Council on 29 April," writes Mosley, according to Reuters, which has seen a copy of the letter.

"The financial regulations will be based largely on the principles established by the teams and the FIA last year. The key point is that the budget cap for 2010 will cover all team spending except for marketing and drivers."

The budget cap is optional, however, those teams that do not accept it will face greater technical restrictions than those teams that do. Already, American newcomer USGPE has said it will accept the cap, while Lola and David Richards are also keen.

In addition to these three, Pitpass, as previously reported, is aware of several other potential new entries, thought to include, Dallara (possibly with ART), Nick Wirth, Racing Engineering and Colin Kolles, in partnership with Franz Hilmer of Formtech GmbH, the company that bought Super Aguri. However, only three teams will be accepted.

"Apart from the three new teams, we have had indications that some existing teams would like to run under a cost cap in 2010," added Mosley

"This might mean an adjustment of the 30 million figure," he continues. "Could you, therefore, please indicate what you would consider to be a minimum acceptable figure for the cap?

"World economic conditions and the outlook have deteriorated considerably since cost cap targets were discussed last year," adds Mosley. "As a result, it is likely that without the opportunity to participate under a cost cap, we will lose at least two further teams for the 2010 season, notwithstanding the cost-saving measures which FOTA has already agreed. This would leave us with just 16 cars.

"However," he continues, taking yet another swipe at the Formula One Teams' Association, which has said it will be able to secure an engine and gearbox supply next year for £5.8m (6.5m euros), "the FOTA cost savings have been achieved at a pace which suggests that teams can adjust much more quickly than was apparent 12 months ago."