Procter & Gamble and Unilever have been fined 315 million euros for price-fixing.
There are much more imaginative (and legal!) ways to maintain a price premium than this. Product innovation enables price differentiation; increasing the perceived value of your product allows you to charge more; and bundling your products in innovative ways can reduce commoditisation.
I know that Unilever at least is engaging in some of these things, and I’m sure P&G must do too. Naturally I am available to assist with behavioural pricing research if either company is interested in a chat…