The Conservative party would require 40% of those eligible to vote for strike action to do so among certain ket service workers, it was announced on 9 January 2015.
Those affected include teachers, nurses, firemen and transport staff.
A separate earlier proposal would require a turnout of at least 50% for any strike ballot.
The party is considering banning strikes completely in certain areas, as they already are for police and military.
Another proposal is to allow agency staff to cover for striking workers.