Any announcements on dates will only be made next week at the earliest.
I've just had a quick google and it seems they're thinking of strike action because they have had no pay increase since 2008, and the current pay offer is below inflation (therefore a cut). The current dispute has been grumbling on for about 18 months, and it seems they're reached the "enough is enough" moment.
They've already been on a pay freeze since 2008, and seem to be calling for something in line with inflation. So it's not a pay increase, rather a "stay put" respite after 3 years of fall in real terms.