Well there's 2 sides to it I suppose. 1. Business' labour costs go up so to maintain their margins their prices will go up. 2. People have more disposable income so there is more demand and if the supply doesn't increase accordingly then prices go up.
The theory is fine but in reality this inflation isn't caused by people's income leading to excessive business costs or excessive demand, it's caused by Brexit costs to business, the effect of the pandemic on the supply of goods, wasteful government spending and fiscal policy as well as some misguided central bank policy during the pandemic, profiteering by oil and energy companies, and political disputes between the West, Russia and China.
So effectively they're saying "well we're not letting the mega rich suck up the cost of all this poor policy and unfortunate global circumstances, you're going to have to suck it up normies and to hell with whether the economy ever grows again, real terms pay cuts and tax rises all round".