WASHINGTON (AP) — The chairman of a House oversight panel is questioning whether Commerce Secretary Wilbur Ross was "truthful" when testifying last year about his decision to add a citizenship question to the 2020 census.

Democratic Rep. Elijah Cummings of Maryland says documents show Ross engaged in a secret campaign to add the question from the first days he joined the Commerce Department.

Ross testified Thursday before the House Oversight and Reform Committee. He is sticking with his contention that Justice Department officials made a formal request to include the citizenship question to help it enforce the 1965 Voting Rights Act.

Some 18 states, 15 big cities or counties, and immigrants' rights groups have sued the Commerce Department, claiming it failed to properly analyze the effect of the question on households with immigrants.