The bitter rivals have come together in India to lobby the government on regulations that threaten to dampen their expansion ambitions. Among other things, the giant retailers are asking for an extension on a Feb. 1 deadline for implementing those rules, according to people with knowledge of the matter.

The newly tightened regulations threaten to pinch Amazon and Walmart’s Flipkart in one of the world’s fastest growing online commerce arenas, where both have invested billions of dollars. They require online marketplaces to treat all vendors equally, effectively barring foreign companies from featuring exclusive products on their platforms, owning inventory, and thus being able to influence pricing and offer huge discounts.

In addition, Amazon and Flipkart get a lot of their Indian inventory through companies they own or back, goods that’re then sold directly or through favored merchants. One such seller is Cloudtail, owned by a joint venture between Amazon and a company run by Infosys Ltd. billionaire co-founder Narayana Murthy. As rules stand, the two American…