It comes days after the Yorkshire-based supermarket was taken off the stock market following the £7 billion acquisition.
The Competition and Markets Authority (CMA) has served an initial enforcement order on Morrisons, CD&R and Motor Fuel Limited, the forecourt giant also owned by the US investment group.
In the order, the regulator said the parties must remain separate and hold off integration plans until the probe has taken place.
It is understood that the CMA is particularly keen to investigate whether there could be competition issues surrounding Motor Fuel’s petrol station sites and Morrisons’ own forecourts.
CD&R bought the Motor Fuel Group in 2015 for £500 million and has grown the forecourt operator to around 900 filling stations across the UK.
Meanwhile, Morrisons operates around 335 fuel outlets, meaning CD&R would control more than 1,200 of the UK’s roughly 8,000 petrol stations.
The CMA could investigate the deal in a similar fashion to its inquiry into Asda’s takeover by EG Group owners Mohsin and Zuber Issa and private equity backer TDR Capital.
Asda agreed to sell 27 petrol stations to assuage concerns from the CMA that the company could raise fuel prices in these specific locations, which were in close proximity to EG group sites.
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