From Noah Efron's Real Jews: Secular Versus Ultra-Orthodox: The Struggle for Jewish Identity in Israel (p. 177):
[Journalist Shahar] Ilan recounted that use of amulets and blessings as electoral assets was pioneered in 1988 by representatives of the Lubavitcher rebbe, Menachem Schneerson, working to enlist votes for Israel’s Agudat Yisrael party. Aryeh Deri, the former leader of Shas who was imprisoned for financial irregularities and breach of trust (which I will soon describe), explained the modus operandi of the Lubavitchers, from which he would learn important lessons for the elections that followed:
They would have a person sign a letter to the Lubavitcher rebbe, in which they committed to voting for the Agudah. The next day, someone would call the same person, presenting himself as a pollster for a public opinion research center, asking how the person planned to vote. If he answered with some other party, they would later call him again, this time in the name of the Lubavitchers, and say, “We sent your name by fax to the Rebbe in New York, and we received a reply that you’re unreliable."
This tactic combined spiritual carrot and stick: blessings for compliance, and the Rebbe’s omniscient wrath for noncompliance. For people who care about this sort of thing, it was powerful incentive to vote the way the Rebbe (or, at least, his representatives) wished.