In the negotiations over the past two years, it is understandable that table 2 union members had no hesitation using their right to strike, which they had obtained on December 16, 1998. So, in a perfectly legal context, the union is exercising its means of pressure by holding rotating strikes across the country since January 18.
The union has been holding strikes since the spring 
( z1 strike :ARG0 ( z2 union ) :time ( z3 since :op ( z4 date-entity :season ( z5 spring ) ) ) )