关于If条件状语从句中,什么情况下主句中用一般现在时.

关于If条件状语从句中,什么情况下主句中用一般现在时.
The fising unions are negotiating with their employers for a pay rise.If there is no agreement by next week,they are threatening to strike and are even talking about blockading ports around the country.这个句子百分之百是对的!但我想知道为什么不是they will treaten to strike...或者用will be striking 按我的理解,主句至少用将来时,可这个句子为什么是现在进行时呢?