Americans will be asked about their citizenship in the US census for the first time since 1950, in a move which opponents fear will damage the process of fair elections.
It comes after President Donald Trump claimed, without supplying any evidence, that millions of illegal immigrants fraudulently voted in the 2016 presidential election.
The US constitution requires a census to take place every decade and forms the basis for election maps and the distribution of funding.
The government has announced it will include the controversial question on citizenship status in the next census in 2020 which could have major political ramifications for how election maps are drawn.
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Officials say the move will help the US government enforce the Voting Rights Act and give it the figures it needs to allocate resources.
But opponents have argued it will discourage migrants from responding, leading to populations being under counted and states with higher immigrant populations losing seats in Congress and electoral college votes in presidential elections.
The state of California is suing the Trump administration over the move, arguing it is unconstitutional because it would stop the federal government from being able to conduct a full count of the US population.
The state’s attorney general, Xavier Becerra, said: "The census has a specific constitutional purpose: to provide an accurate count of all residents.
“California simply has too much to lose for us to allow the Trump Administration to botch this important decennial obligation. What the Trump Administration is requesting is not just alarming, it is an unconstitutional attempt to discourage an accurate census count.”
The lawsuit forms part of a broader political debate between the Trump administration and many Democratic controlled states which fear the move will simply serve to strengthen the Republican Party’s position in future elections.
Voter swing map
Republicans gained a significant advantage in redrawing maps after the 2010 census and Democrats fear a similar move after the 2020 census could see political power shift from cities to more rural communities, which would work against them.
The commerce department, which oversees the census, said it had reinstated the controversial question after a request from the justice department.
Wilbur Ross, the commerce secretary, argued that the move actually protected immigrants as the Voting Rights Act required a tally of citizens of voting age to ensure that minority groups were not discriminated against.
He added that even if the citizenship question had an effect on responses, "the value of more complete and accurate data derived from surveying the entire population outweighs such concerns".
Sarah Sanders, the White House press secretary, said the question "helps us comply with the Voting Rights Act".
She added: "That information needs to be gathered and has been included in the census every time since 1965 with the once exception of the 2010 status.
"This is something that the commerce department felt strongly about."
However Eric Holder, the former US attorney general who serves as chairman of the National Democratic Redistricting Committee, said the decision could lead to “devastating, decade-long impacts on voting rights and the distribution of billions of dollars in federal funding.”