The likes of VW, Porsche, BMW and Mercedes-Benz have halted sales of certain plug-in hybrid models throughout Europe due to the new WLTP emissions regulations.

Known as the Worldwide Harmonized Light Vehicles Test Procedure (WLTP), the new standard went into effect in the European Union this month, pushing certain PHEV models over the 50 grams per km CO2 emissions threshold, reports Automotive News Europe.

This means that cars are liable to lose tax benefits offered in many European countries, defeating the purpose of owning a hybrid vehicle.

Meanwhile, VW has had to stop sales of their mid-size Passat GTE model, Europe’s second best-selling plug-in hybrid, as well as the Golf GTE, the continent’s fourth best-selling PHEV.

A spokesman for the company said that VW plug-in hybrid models were at the back of the line for WLTP testing, behind more conventional cars. “There is a bottleneck with the testing,” he said. “We have to get priority for highest-volume models,” meaning petrol and diesel cars.

Porsche have also pulled sales for its plug-in hybrid Panamera and Cayenne models, as their spokesman stated that the Stuttgart brand won’t begin “taking orders again until the cars are being built, the timing of which has not yet been confirmed.”

As for BMW and Mercedes, both automakers are working on launching more efficient PHEV models within the next few months, which will emit under 50g/km of CO2.