"I think it's a real tragedy for New Zealand is effectively what RNZ is proposing to do is ... turn it into a jukebox."
A petition calling for RNZ to ditch its plans to scrap Concert has already received 10,000 signatures.
All 18 jobs at Concert will be made redundant but 17 new jobs would be created at the new, yet-to-be-named, channel.
The move means Concert would lose its FM radio slot and all its presenters.
RNZ said shifting Concert to the AM frequency would free up space for the broadcaster to build a new music brand for younger audiences.
But Clark said the reasons given by RNZ's management for scrapping Concert "don't stack up".
"One doesn't have to destroy RNZ's Concert Programme to establish youth radio services and broaden audiences."
After her initial tweet yesterday, Clark was at it again today this time directly challenging the Labour Party.
She pointed out that before the 2017 election, the party's manifesto contained a pledge not to reduce funding for, or the quality of, RNZ's content and delivery including Radio NZ Concert.
She tagged Finance Minister Grant Robertson and Broadcasting Minister Kris Faafoi in the tweet.
Clark even went as far as saying there was a "pattern here of destruction of cultural services available to New Zealanders".
In response, Robertson said he was looking into the issue.
"I am advised it is still a consultation and we will be talking to RNZ about their options."
Speaking to media this morning, Faafoi said he was also looking at ways to mitigate some issues around Concert FM.
Faafoi said that he met with RNZ's board last week and outlined some of his concerned about the proposed move.
