After flagging voters who do not cast ballots in two consecutive federal elections, the Board of Elections mails notices to determine whether voters still live at the address where they are registered. If no confirmation comes back, a voter can be deleted from the rolls. Board positions are equally split between Republicans and Democrats; each voter removal must be approved by both a Republican and a Democratic employee, according to the rules.

It remained unclear at what point employees at the Brooklyn office stumbled, or who was at fault. One possibility was that the notices to voters were mailed incorrectly, or not at all. Another was that once the notices were returned, the computerized database that held voter lists was mishandled.

On Thursday, the Board of Elections announced that it had suspended a longtime employee, Diane Haslett-Rudiano, the chief clerk at the Brooklyn office and a Republican appointee. Ms. Haslett-Rudiano’s Democratic counterpart, Betty Ann Canizio, who would, by the rules, be required to sign off on any voter removals, remained in her post. Board officials have declined to say why Ms. Haslett-Rudiano was disciplined, saying at the same time that “no voters were disenfranchised.”

“There was criticism that the voter rolls had people who were dead, and so on,” said Frank Seddio, the chairman of the Brooklyn Democratic Party, who said he had discussed the apparent mistake with Board of Elections officials. “That began a citywide review of who’s on the voter rolls and who should be removed. And there’s a possibility that people were taken off the rolls that shouldn’t have been taken off the rolls.”

It is only the latest trouble of many for the board, a frequent target of elected officials, government watchdog groups and election law experts, who say blunders are inevitable when an organization is run from top to bottom by political patronage appointees and party members, as the board is. A 2013 report from the New York City Investigation Department found that the board was plagued by nepotism, badly trained poll workers and error-prone voter-removal procedures.