At a time when election officials are struggling to convince more Americans to vote, advocates for the disabled say thousands of people with autism spectrum disorder, cerebral palsy and other intellectual or developmental disabilities have been systematically denied that basic right in the nation's largest county.

A Voting Rights Act complaint to be filed Thursday with the U.S. Justice Department goes to a politically delicate subject that states have grappled with over the years: Where is the line to disqualify someone from the voting booth because of a cognitive or developmental impairment?...

At issue in the California case is access to the ballot box for adults who enter so-called limited conservatorships, legal arrangements in which parents or guardians assume the right to make certain decisions for people who lack the ability to manage their financial and medical affairs. In the course of taking that step in court, voting rights are routinely voided, according to the advocacy group.

California has over 40,000 such cases, and those covered by the arrangements usually live with their families or in group homes. A recent sample of 61 cases by the advocacy group in Los Angeles County found that 90 percent of the people covered by limited conservatorships had been disqualified from voting.