https://ballotpedia.org/Voter_caging_and_purging
Voter caging
Voter caging is a tactic that specifically refers to times when a political party or another partisan organization sends registered mail to addresses of registered voters that they have identified as likely to be unfriendly to their candidate. All mail that is returned as undeliverable is placed on what is called a "caging list." The group that sent the mail then systematically uses this list to challenge the registration or right to vote of those names on it, on the grounds that if the voters were unreachable at the address listed on his or her voter registration, then their registration is fraudulent, and they should not be allowed to vote.[1]
Challenging voter caging
The process of issuing the challenges differs from state to state. Commonly, though, the process begins with a formal written challenge filed with local election boards by a certain date before the election.[2]
States where voter caging is illegal
Minnesota outlawed the practice of building voter caging lists compiled from returned mail sent by a political party after the 2004 election.[3]
Examples of caging
Michigan (2008)
On September 16, 2008, the Obama legal team announced they would seek an injunction to stop an alleged caging scheme in Michigan wherein the state Republican Party would use home foreclosure lists to challenge voters still using their foreclosed home as a primary address at the polls.[4] Although Michigan GOP officials called the suit "desperate," a judge found the practice to be against the law.[5][6]
Louisiana (1986)
A 2004 article in the Washington Post stated, "In 1986, the Republican National Committee tried to have 31,000 voters, most of them black, removed from the rolls in Louisiana when a party mailer was returned. The consent decrees that resulted prohibited the party from engaging in anti-fraud initiatives that target minorities or conduct mail campaigns to 'compile voter challenge lists.'"[7]
New Jersey (1981)
A 2004 article in the Washington Post stated, "In 1981, the Republican National Committee sent letters to predominantly black neighborhoods in New Jersey, and when 45,000 letters were returned as undeliverable, the committee compiled a challenge list to remove those voters from the rolls. The RNC sent off-duty law enforcement officials to the polls and hung posters in heavily black neighborhoods warning that violating election laws is a crime."[7]