According to RMTs info to train staff:

"The RMT has ordered two days of action to highlight safety on the tubes.
On these days, train operators will drive at a maximum of 35 miles an
hour. On areas of track of particular concern, drivers will be advised to
drive at lower speeds.
This will affect the entire network as the union believes that there are
no areas that are up to standard.
This is because in preparation for the introduction of PPP London
Underground allowed the ongoing deterioration of track.
The action will commence on December the 8th until close of traffic on
December the 9th"

Roger