SAN FRANCISCO, Aug. 2 (Xinhua) -- San Francisco Mayor London Breed and California Assemblyman David Chiu Thursday joined immigrant advocacy groups to urge the city's residents to oppose U.S. President Donald Trump's administration for its plans to question citizenship status in a national census in 2020.

During a tour to Chinatown in downtown San Francisco, Breed and Chiu called on the city's residents to participate in the public comment period for the 2020 Census in which Trump's administration plans to include a question about citizenship status on the upcoming census.

"The Trump administration wants to weaponize the Census to intentionally under-count minority and immigrant populations," said Mayor London Breed.

"It is anti-Democratic, un-American, and fundamentally unjust. The time for action is now," said the first African-American female mayor of San Francisco, who took office on June 13.

The Commerce Department, which administers the nationwide head count every 10 years, said in March that it would place the citizenship status issue on the upcoming census, and some federal officials claimed they needed the information to enforce voting rights laws.

But California officials insisted that the government's move would lead to an undercount in the state, which is home to a large number of foreign-born immigrants, who may be scared off from the upcoming census.

Experts and demographers, including the Census Bureau's own researchers, have also predicted that the inclusion of a citizenship question could decrease census participation among undocumented immigrants, documented immigrants, and others in their households and networks.

Chiu, a Democrat in the California State Assembly representing the 17th Assembly District, which encompasses the eastern half of San Francisco, slammed the Trump Administration's "attempt to use the census, which is traditionally a non-partisan function of government, as a tool for political gain," which he said is unethical and illegal.

"Everyone who cares about living in a free and fair democracy should raise their voice and oppose the citizenship question," he said.

A significant undercount in diverse states like California and hard-to-count urban centers like San Francisco will lead to an extraordinary loss in federal funding and result in inaccurate and inequitable representation at the federal, state, and local levels of government, supporters of the immigrant advocacy groups said.

An undercount in the 2020 Census would also negatively impact private businesses and the healthcare industry, which rely on accurate federal government data, they said.

Multiple lawsuits across the country have been filed against the U.S. Census Bureau and the Department of Commerce challenging the legality of the citizenship question. California and San Francisco have also taken similar legal action against the issue.