IMP had a good run since the start of the month, perhaps in anticipation of the end of the strike. I would therefore suggest that there are profits being taken. (Buy on rumour, sell on fact.) What is of some concern for both IMP and AMS is that they have had to agree to substantially above-inflation multi-year increases.
I must add that every day that AMS goes up, it surprises me. It is trading at 5 x NAV (IMP is < 3 x NAV), and the estimated P/E for the next three years is horrible (58, 51 and 28 for AMS, vs. 21, 16 and 12 for IMP).