A can't raise. the rule you want from robert's rules is
An under-raise happens when a player goes all in and in doing so has raised the bet but not by the full
amount necessary. When this happens the betting becomes ‘locked’. Any players that have already
acted in the hand (called, checked, bet etc) may not re-raise. Any players that have not yet acted may
raise as normal if they wish
perfect
the minimum raise in any situation is always the the amount raised to-previous call. for example
at blind level 100/200
player A bets 600, player B raises to 1600, back to player A, the minimum raise he can make now is to 2,600
600 with 1000 with 1000.
if player A in fact decides to raise to 3000, Player B's minimum raise is to... 4,600
600, with 1000, with 1400, with 1400 = 4,600.
Not always the case lildave. i remember Vicky Coren and the late George Geary coming to blows in the first Ukipt season at G in Manchester. iirc G casino rules said the raise had to be min twice the previous bet as opposed to the "with" rule that is most commonly used. As it was A ukipt tourney Vicky was given the nod eventually but she had to go above the TD who gave the original ruling to George and the double the raise rule.
Author