The relationship between Red Bull and Renault has been a rocky one since the introduction of new power unit regulations in 2014.
Red Bull bosses Christian Horner and Helmut Marko were critical of their partner in the second half of 2016, threatening to withdraw from the sport if it could not get a supply of competitive power units.
Since then, the Austrian drinks company's junior team has this year adopted Honda engines in a move regarded as a precursor to the senior Red Bull team taking up a supply for 2019, if the engine proves competitive.
“At the end of May there needs to be some clarity as to who is supplying which team, which supplier is supplying which customer team. As far as we are concerned, that will be the deadline,” asserted Renault boss Cyril Abiteboul.
“We are not going to hang around forever,” he added.
“But one thing that is clear is planning and there will be a deadline for Red Bull Racing to define what they want for the future. It's available, it's in the Sporting Regulations.”
Red Bull has used Renault engines since 2007, though a naming rights agreement saw the power units rebranded as Aston Martin from the start of 2017.
The 2018 F1 season got underway in Barcelona earlier this week with the first of two four-day pre-season tests.