What would be a “slap in the face“?
a) A pay freeze for local authority workers
Unison say:

The decision to cut our members’ pay without negotiation is a slap in the face for hard-working council employees who have kept local communities together through the financial crisis.

or
b) An inflation-busting 2.5% pay rise for local authority workers paid for out of our council taxes (inevitably either through a tax rise or decreased services)
The Local Government Employers say:

Councils are facing a perfect storm of falling revenues and increasing demand for services.
Up and down the country, …

Even the Trade Unions can see where the political tide is going – towards the Conservatives – that is why they are discussing with their trade union envoy.
However, there appeara to be some who either (a) are complete idiots, or (b) really want the Conservatives to win. Why? Because they are threatening a new Winter of Discontent.
Trade Unionists don’t appear to learn from history, do they? Either that or even they have defected from Brown.

Certainly that will be the case if this happens:

Unions are to demand new rights to strike as the price for keeping the cash-strapped Labour Party afloat.
Repealing the ban on secondary industrial action is among a swath of left-wing policies that unions want to see in the Labour manifesto. The pressure on Gordon Brown comes as he is relying on the unions to help to avert Labour’s cash crisis, when they are in increasingly militant mood…
As unions begin to flex their muscles on the ground, they are working to maximise their …

The Labour Party, and thus the British government itself, is currently massively in debt to the trade unions. Not just purely financially either.
The unions, in addition to paying £10 million into Labour’s general election war chest, pumped carefully targeted resources into specific marginal seats for the first time.The Daily Telegraph can disclose that the unions paid for six million direct mail shots, organised a postal vote recruitment campaign, provided teams of drivers, set up a nationwide website and sent almost 200 campaign officials to the marginal seats.The logistical support, which …