In the US, this - "They made a pact to pull out of Gold and other discount programs for a few days." is collusion and is illegal.

If FTC allows restaurant owners (or any group of businesses) to create pacts like this against their suppliers or customers, next time, they will make similar pacts against you (the customer). "hey, what say, let's all make a pact together and increase the price of that dosa to $50?"

In reality, some industries (most famously airlines) do this kind of collusion through winks and nods anyway and is bad for consumers (very good for the industry as a whole though).

If they want to get together and form a group dedicated to the principle of "give us more money", that's cool (to the extent that Indian antitrust law allows it) and I have no objections. But they won't get much media traction that way.

What they're doing instead is telling the media they've been cheated - that they deserve more money, and Zomato's acting unethically by giving them the advertised service for the agreed price. I'm not sure that's an honest way to look at the situation.