Formula One's governing body has made teams a final offer, with changes to the controversial 2010 rules, in an attempt to stop the sport from tearing itself apart.
Five of the existing 10 teams -- championship leaders Brawn, BMW-Sauber, McLaren, Renault and Toyota -- risk exclusion if they do not sign up by tomorrow morning.
If they don't there is a risk of them setting up a rival series with champions Ferrari and the two Red Bull teams also at loggerheads with the International Automobile Federation.
Both sides, however, are making last-ditch efforts to reach a compromise deal.
President Max Mosley has set out what the FIA is willing to concede in return for unconditional entries.
The terms effectively cement agreements reached before talks broke down this week, when the FIA said the regulations remained in force and accused the teams of wanting to take over the sport.