Agreed, this is more of just a bargaining tool that the pilots have thrown into the ring in the negociations. They won't strike on the busiest weekend of the year, most journeys for that weekend will likely have already been booked as this is being announced 6 weeks ahead so it looks like they're attepting to limit any damage to the company, whether the strike goes ahead or not, other then the last minute bookers.
I don't think you can deny them their increments if it was part of the deal for the 5 year pay freeze and 12% pay cut, that they'd get them back this year, they've made a profit for the past 4 (5?) years, so the management don't really have a leg to stand on in denying them the increments.