The employment minister, Michaelia Cash, has struggled to explain exactly how Victoria’s Country Fire Authority is being subjected to a “hostile union takeover” in a new pay deal struck by the Victorian Labor government.

She has also failed to say how an individual volunteer firefighter in Victoria will be affected by the deal, despite the Turnbull government’s vehement opposition to it.

Cash unveiled the government’s proposed changes to the federal Fair Work Act on Monday with the prime minister, Malcolm Turnbull.

In a joint statement, the pair said the Victorian Labor government was seeking to hand control of Victoria’s CFA volunteers to the United Firefighters Union through a new enterprise agreement that clearly discriminated against volunteers and provided the UFU with an “unreasonable, unwarranted degree of control over volunteer operations”.

They said their proposed changes to the Fair Work Act would prevent that from happening, while also stopping “similar union takeovers” from happening to volunteers of other firefighting and emergency services bodies covered by the Fair Work Act.

But appearing on Sky News on Monday afternoon, Cash had trouble explaining exactly how the Victorian government’s enterprise agreement would adversely affect a CFA volunteer.

Asked by host David Speers what clause she found most worrying in the enterprise agreement, Cash said: “There is no one clause, David. There is no one clause.”

When Speers asked what the impact of the agreement would be on “a long-serving, very honourable, hard-working” volunteer, Cash replied: “Well you’d need to ask that person.”

So Speers pressed the minister: “I’m just asking, you’re the one wanting to intervene here.”

Cash replied: “You’d need to ask that particular person, but certainly they feel so affronted that many have said they will resign, or are already resigning.”

She then criticised the Victorian government’s pay deal for creating so much confusion, and for making CFA volunteers feel as though their autonomy had been taken away from them.

The Greens’ employment spokesman, Adam Bandt, said the interview was a “train wreck” and Cash ought to resign.

“This fumbling, bumbling, train wreck of an interview confirms why the Minister must go,” Bandt said.

“Having been forced to acknowledge her lies in the morning, by the evening the minister could not point to any specifics in the enterprise agreement to sustain her scare campaign.

“Her untruthful fear campaign exposed, the minister resorted to waving around the legislation and saying how few pages it has.”

Earlier on Monday, Cash had been forced to apologise for an opinion piece she wrote for the Herald Sun in which she claimed the controversial enterprise agreement required “seven paid firefighters (ie union members) to be present before CFA personnel are able to be deployed to a fire”.

In fact the proposed agreement only requires that seven paid firefighters be dispatched, meaning it does not prevent volunteers fighting fires if they arrive first.