Who has forbidden Katniss' 'Hanging Tree' song?

Question

In the Mockingjay book in the Hunger Games series Katniss sings a song called 'The Hanging Tree'. She mentions that the song is actually forbidden:

I have not sung "The Hanging Tree" out loud for ten years, because it's forbidden, but I remember every word. I begin softly, sweetly, as my father did.
_{-The Hunger Games: Book Three - Mockingjay, Part One - "The Ashes", Chapter Nine.}

At first I thought it was the Capitol itself that had forbidden the song, however, after Rand pointed out in a comment on my related question (What does Katniss' song “The Hanging Tree” mean?), it could actually have been Katniss' mother who forbid the song.

Was it Katniss' mother or the Capitol who has forbidden 'The Hanging Tree'?

Answer 1

It was most likely forbidden by the Capitol, although this is never stated explicitly

Katniss' mother, does however personally forbid her husband and possibly Katniss from singing it

Katniss recalls some memories from the song, including her dad singing it to her in the woods. Recalling that her and her sister would make necklaces out of rope without truly understanding the meaning of the words:

In the stillness I remember the scene. I was home from a day in the woods with my father. Sitting on the floor with Prim, who was just a toddler, singing "The Hanging Tree." Making us necklaces out of scraps of old rope like it said in the song, not knowing the real meaning of the words.
_{The Hunger Games - Mockingjay: Chapter 9}

Katniss' mother was clearly outraged by the imagery of the lyrics reflected on her daughter making rope necklaces (recall the singer, who was hanged, is calling their lover to hang with them and join them in death) that she began to scream at her husband.

Suddenly, my mother snatched the rope necklaces away and was yelling at my father. I started to cry because my mother never yelled.
_ibid.

Katniss' father finally explains that the mother doesn't want to hear the song and that they are no longer to sing it.

He calmed me down and told me everything was fine, only we'd better not sing that song anymore. My mother just wanted me to forget it. So, of course, every word was immediately, irrevocably branded into my brain.
_ibid.

It would appear that Katniss' mother simply wanted to protect her daughters' innocence and ensure they didn't get into any trouble singing it in public without fully understanding the lyrics.

I guess my mother thought the whole thing was too twisted for a seven-year-old, though. Especially one who made her own rope necklaces.
_ibid.

This would make it seem like Katniss' mother forbade it, which is possible, however, most discussion seem to agree that it was "forbidden" by the Capitol, and Katniss' mother as a healer didn't want to see her husband's back whipped.

I have not sung "The Hanging Tree" out loud for ten years, because it's forbidden, but I remember every word.
_ibid.

As @DanielB mentions in their answer, the term forbidden is most commonly used in reference to the Capitol forbidding things. This however does not leave out the possibility that Katniss' mother's reaction led Katniss to convince herself it was forbidden, even if the more unlikely scenario.

Further reasons for the banning of the song may include its role as a song for the rebellion. It is likely Katniss' father sang it to let others in his district know that he was willing to rise up against the Capitol and that they should join him. This is similar to songs in our history, such as Strange Fruit by Billie Holliday becoming a civil rights movement anthem in the 50s and 60s.

Answer 2

The phrase "forbidden" is pretty consistently used to refer to the Capitol.

All forms of stealing are forbidden in District 12. Punishable by death.

Hunger Games p. 30.

I have to remind myself that he’s still not used to the woods, that it’s the scary, forbidden place beyond the fences of District 12.

Hunger Games p. 310.

Some of the stations teach survival skills, others fighting techniques. We are forbidden to engage in any combative exercise with another tribute.

Hunger Games p. 93

The woods, of course, are forbidden.

---

Then, for a week, there was a lockdown. No food, no coal, everyone forbidden to leave their homes. The only time the television showed anything but static was when the suspected instigators were hanged in the square

---

“I'm not sure. I just wanted to hold them accountable, if only for a moment,” says Peeta. “For killing that little girl.” “This is dreadful.” Effie sounds like she's about to cry. “That sort of thinking ... it's forbidden, Peeta. Absolutely. You'll only bring down more trouble on yourself and Katniss.”

Catching Fire.

Moreover, considering her mother was catatonic for a while, I can't imagine that she had the authority to forbid anything in a way Katniss would listen to.

Answer 3

It was likely forbidden by the Capitol

I have not sung "The Hanging Tree" out loud for ten years, because it's forbidden, but I remember every word.
_{—Mockingjay, Chapter 9, by Suzanne Collins}

The crucial words here are "it's forbidden". It is forbidden.

Had her mother forbidden her to sing the song, she would not have expressed it like that. She would've said "my mother forbade me" or something similar.