By Alan Baldwin
LONDON (Reuters) - Formula One teams will have to reach unanimous agreement in the coming weeks if the sport is to expand to 21 races next year and manufacturers are to be allowed to supply customer teams with older engines.
The latest draft calendar has 21 races, including a new grand prix in Azerbaijan, but the 2016 sporting regulations published on Wednesday stipulate, as ever, that "the maximum number of events in the Championship is 20".
The definitive calendar will not be published until December.
Any changes to the published regulations can now be made only "with the unanimous agreement of all competitors entered in the 2016 championship, save for changes made by the FIA for safety reasons".
Teams are likely to approve an expanded calendar if it brings them more money but allowing the use of older engines is more controversial.
"Only power units which are identical to the power unit that has been homologated by the FIA ... may be used at an event during the 2016-2020 Championship seasons," declares the revised article 23.5.
That would prevent manufacturers from supplying older versions to some customers, as has been the case this year with tail-enders Marussia given permission to use 2014 Ferrari engines after coming out of administration.
Marussia will switch to Mercedes engines next year but Red Bull-owned Toro Rosso are negotiating to use 2015 Ferrari engines in 2016.
Sister team Red Bull Racing, who have fallen out with current partners Renault and been rebuffed by champions Mercedes, have threatened to walk away unless they can secure a competitive engine of the latest specification.
Changes to the technical regulations have also raised the possibility of a return to exhaust-blown aerodynamics with multiple tailpipes from next season instead of the sole exhaust.
"Engine exhaust systems must have only a single turbine tailpipe exit and either one or two wastegate tailpipe exits," the new rules say.
(Reporting by Alan Baldwin, editing by Neville Dalton)