The class of debtholders that would gain control would vary. It is usually the class that would receive partial payment if there was a liquidation (with the more junior class getting zero, and the more senior class getting full payment).

The tightest debt covenants belong to the senior bank financing. They will look at a firm in crisis and ask the following: if we let this run, how likely and how big would any impairment of capital be? If we waive the covenants for now, what payment or additional security can we receive? Let the junior debt suffer, we are in the driver’s seat.

Those that offer junior debt financing are often at the mercy of the banks on the one side, and the private equity on the other. They rarely get control unless the company goes through the bankruptcy process.

If it turns out that the senior holders have control, presumably they’d be inclined to call a deteriorating play early. Junior holders would be 100% at risk early in the process, so would presumably try to push default into the future, even if it prejudices the position of senior holders.