Temporary... until the dust settles. Back in the '87, crash.... Refco raised the margin to $50,000 for the pit S&P contract, and said "we'd prefer our customers not trade the SP Futures for the time being."
this is a terrible broker.. leave them... if you strategy requires a stable margin req.. you should not be with IB
They raised margin requirements on VIX products too, and warned you well in advance. They do this kind of thing around major political events each time. It shouldn't be unexpected and arguably it's not unreasonable either. They don't owe you the right to borrow lots of money from them all the time just because you wish they would. Of course if you prefer a different broker, it's a free country and you don't have to do business with IB. Best choice for me, occasional limitations like this not withstanding.
The risk is their algorithm decides your SPX options positions should be liquidated and they do it for you at the market.
I doubt they can warn you well in advance. I doubt they have special ability to foresee the events any better than other investors. But what happens if you already have open positions? They would liquidate them at the most inconvenient time ?