Signing a card doesn’t vote in a union, it’s a petition to have a vote  

The card can be solicited for a whole year from employees.  Once signed, it is held even if the employee moves on or changes his mind.  If the union can obtain 50% signed cards, they will attempt to claim they have succeeded in establishing a union without an actual vote and hope the company doesn't contest it.  If the company doesn't contest, thenunion will claim itself without an actual vote.   If the comp does contest, the matter comes up for a vote BUT the union now has gained a huge strategic advantage because it only needs a majority of those voting to win.  Of course, those anxious to establish a union will vote.   But, those who are not anxious to start a union and don't participate in the hoopla will be counted as an abstain where their nonparticipation will count against them.   

usually, to establish something when there wasn't anything, it requires a majority of the whole.  IOWs, it would take a majority of all to vote to establish itself.   But, now, having collected cards for a whole year, the union can established itself with just one person voting FOR a union, with the other 99% ignoring the vote by not participating.   A HUGE advantage for unions to gain access when they had little chance in reality.  

Beware of the used car salesman  tactics here!