An internal memo is to be sent to 200 Railtrack staff in Swindon warning them they will not be allowed to be seen "whooping it up" this Christmas.
The firm says it is in "corporate mourning" in the wake of the Hatfield crash and has cancelled all official parties.
The notice was aimed mainly at staff at the firm's office in York where the Hatfield train had been heading for but all regions will be receiving a copy.
It said: "In the aftermath of Hatfield, Railtrack is in corporate mourning and will be for the next few weeks.
"As such, any Christmas celebrations which involve contributions by Railtrack or booked in Railtrack's name must be cancelled."
Four people died and 35 were injured when an express train derailed at Hatfield, Hertfordshire, a month ago.
Staff will still be allowed to organise events booked in their own names and in their own time, as the staff at Swindon's Gloucester Street office have done.
But the office itself is set to remain devoid of Christmas cheer as a mark of respect to the crash victims.
"We need to consider the feelings of the families of the bereaved and the injured plus those others on the crash train," the memo continued.
"If we were in their shoes we wouldn't take kindly to railway staff apparently whooping it up in the company's name, particularly when so many of them have little to look forward to this Christmas."
Railtrack Great Western Zone spokeswoman Jane Terry said the Swindon office would follow national policy.
She said: "Staff in Swindon will celebrate Christmas in their own time at their own expense but I think they appreciate it is important to remain sensitive when acting in Railtrack's name."
But a spokesman for the firm's national headquarters said no official parties have been organised in Railtrack's name for three years anyway.
He said: "We're not saying to our staff not to go out and enjoy themselves but to be sensible.
"We don't want to cause any unnecessary upset and this is just a general reminder to respect the sensitivities of the people affected."
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