The general secretary of the PCS's decision to use union funds to back anti-austerity candidates has been four years in the making.
"It is not something that has been done lightly or on the spur of the moment," Mark Serwotka explains.
"Under the last Labour government, there was a feeling in the union that [the party] wasn't really operating in a way that was acceptable to us as public sector workers.
"It led us to the conclusion that there must be times when it would help us get our message across to give people a fairly radical alternative at the ballot box."
As a result, the PCS announced at the weekend that its members voted four-to-one in favour of using its political cash-pot to field candidates that offer a "radical" and "anti-austerity" message.
The union insists it is not the launch of a political party, although they may challenge Labour candidates that do not share their vision.
It will enter this new political dimension cautiously.
"It's fair to say that when we started, we probably had the idea that we would see widespread electoral challenges," explains Serwotka.
"How it has been refined is that it's more about strategic and exceptional circumstances, in certain constituencies, dependent on factors on the ground."
This will probably mean supporting candidates at by-elections to begin with.
"In the short term, we're fairly clear that this is the exception," says the union boss. "If it was the right by-election, and the right candidate, we would put a lot of resources into it."
But the PCS is developing "an all-the-year-round presence in constituencies".
"It will allow us to make informed judgements when the time comes – and obviously that is not now," says the general secretary.
Some questioned why the union did not simply seek Labour Party affiliation – and wield influence in the same way as Unite or the GMB.
Serwotka insists the sixth-largest trade union will not be wed to one party.
"We think we are at the cutting edge of arguing for political trade unionism. But we don't think political trade unionism has to be party political," he says.
"We do not accept that the Labour Party, given its record over the last 20 years, is the vehicle… the best way to argue for better politics."
He admits that he has not spoken to Ed Miliband or any senior Labour politicians about the move.
The union, however, did speak to lefty Labour MP John McDonnell, who chairs the PCS parliamentary group. "We’ve certainly talked to him about the direction we are going," Serwotka says.
"I imagine that John McDonnell will be one of the first that we will consider supporting because he stands with us on every key question."
A union spokesman said the union would pile on pressure to elect only "genuine Labour candidates". But how do you decide if a candidate is "genuine Labour"?
Serwotka pauses. "That quote was carefully constructed so that it said 'Labour', not 'Labour Party'. The political position in Britain has moved dramatically to the right over the last few decades. And in that sense, it must follow that the Labour Party, as the party of government and opposition, has moved to the right as well."
He continues: "The problem with Parliament as it stands is that it is full to the rafters of people who have never really done a proper job, who have no experience of what life is like at the sharp end and who have come into politics through party machines that are conforming to very narrow interpretations of how the economy should be run.
"And what we want to do is take it back to a period when there was real red water between Labour politicians and Tories… There is now far too little between them. And in terms of ideological arguments they are uncomfortably close on many questions."
This presumably means that the union is unlikely to ever back a New Labour candidate. "I can't imagine we would ever do so, no," replies Serwotka.
Although he is clear that turnout was "not great" – about 20% of the 292,000-strong union voted – the "extraordinary thing" was that four-to-one people were in favour. "A lot of people thought we would lose," Serwotka admits.
"There was a feeling that the civil service is not political and therefore people wouldn't want to go down this route. And that is why I think the result is extraordinary."
The PCS will not rule out backing candidates from other parties, including the Greens. Serwotka himself has voted Green in the past. "We would not be prescriptive," he nods.
"The only thing you can say in absolute certainty is that it is inconceivable to ever think that could be a Tory or a Lib Dem, not UKIP and certainly not parties on the far-right. We are talking about people who are standing up for working class communities."
He also hinted that candidates could come from within his own union.
It's not the first time the trade unions have hit the headlines lately.
Labour-affiliated trade union the GMB became embroiled in an almighty row over its plan to "outlaw" Progress from the party.
Serwotka refuses to accept that the decision to fund political candidates is linked or particularly timely.
But he agrees that trade unions are becoming increasingly political. "I think it is borne out of necessity," he explains.
"A lot of unions are affiliated to the Labour Party, and that's how they've channelled their political views on stuff. I think most people would accept though that under the Labour government's terms, they weren't very successful… The attacks on our pensions started under Labour. We're saying the existing routes clearly are not working."
He says that he wants to see the coalition government defeated at the next election, and that, yes, this would require a Labour victory.
"But what we don't believe that means is that you just give a blank cheque and say, 'All we will do is support people from Labour' because of their shortcoming.
"What this is designed to do is exert different types of pressure in the political arena."
He points to the George Galloway by-election victory in Bradford. "Whatever people individually think of George Galloway, it really reverberated throughout the country because of the scale of what he had done.
"We believe it is possible to be done by somebody, for example, campaigning exclusively against the effects of austerity.
"And it would give the union the opportunity to have a very, very public platform in the political arena to argue for things that nobody else is putting forward."
The PCS's vote guarantees that the next by-election will be very interesting… And that's just how Serwotka wants it.