Tens of thousands of eligible voters in at least six swing states have been removed from the rolls or have been blocked from registering in ways that appear to violate federal law, according to a review of state records and Social Security data by The New York Times.

The actions do not seem to be coordinated by one party or the other, nor do they appear to be the result of election officials intentionally breaking rules, but are apparently the result of mistakes in the handling of the registrations and voter files as the states tried to comply with a 2002 federal law, intended to overhaul the way elections are run.

Still, because Democrats have been more aggressive at registering new voters this year, according to state election officials, any heightened screening of new applications may affect their party’s supporters disproportionately. The screening and trimming of voter registration lists in the six states — Colorado, Indiana, Ohio, Michigan, Nevada and North Carolina — could also result in problems at the polls on Election Day: people who have been removed from the rolls are likely to show up only to be challenged by political party officials or election workers, resulting in confusion, long lines and heated tempers.