I have traded futures in the past but have recently started studying options and finally decided to make my first purchase just to get familiar with how to enter the orders and such, anyway, it is a put butterfly spread on SPX 5 points wide, it was very cheap (it is a low probabilty trade) The debit was .25 for 1 butterfly. Everything was fine until the next day, I'm trading with TD ameritrade TOS, and noticed after I logged in that there was a warning in red text stating 'Regulation T Call $$$.$$' This is a margin account, opened with $5,000 ($10,000 available with margin). Shouldn't this be enough to cover any maintenance margin on this trade? My max risk is only the the $25 dollars I spent. Even if they calculated the differnce in strike prices and used that as margin requirement its only 5 points ($500). Am I completely wrong about this?