Washington (CNN) As coronavirus shuts down large parts of the US economy and millions of Americans limit social interaction , the Census Bureau is preparing to send thousands of workers into communities to assist in the decennial headcount.

While this year's census relies more heavily on collecting responses by phone, mail or online, it still needs an army of people to go knock on doors and interact with people. And though it's early, interviews and anecdotal reports suggest that compared to previous years, the Census Bureau is behind on hiring workers due, in part, to fears of exposure to the virus.

As of February 29, the Census Bureau was paying 23,610 temporary workers . At around this time in 2010, it had about 145,000 temporary workers. While the 2020 Census plans to hire fewer than half the 1.2 million workers it needed in 2010, non-profit groups that help recruit workers for the census tell CNN the current pace of hiring suggests a bigger problem may be at play.

"We are really stressed right now," said David Lee, Vice Chair of the Census Information Centers Steering Committee , a network of non-profits that provide outreach and information regarding the census to local governments, businesses and community groups. "We are very behind in hiring, having difficulty hiring staff and outreach workers," said Lee, who is based in Oakland, California. "Some anecdotally attribute that to fear of exposure to the virus.

In Seattle, where coronavirus has hit particularly hard, the outbreak is already disrupting outreach plans to the elderly, says Joon Bang, Chief Executive Officer of the National Asian Pacific Center on Aging, a Census Information Center.

"Because there's so many unknowns and uncertainties, and the virus is posing some additional layers of challenges, whatever plans we were even thinking about implementing during the census period, that's being challenged too," Bang told CNN.

The Census Bureau relies heavily on a network of Census Information Centers, like the ones where Lee and Bang work, to help recruit local workers. Last week the Census Bureau updated its guidance to these groups, emphasizing the ability for individuals to respond to the census online, by phone or by mail, hoping to reduce the need for in-person follow-up efforts.

But half a dozen Census Information Centers in states hit particularly hard by coronavirus, including California and New York, tell CNN they are still concerned about planned person-to-person outreach efforts and say they need more specific guidance.

The Census Bureau has set up an internal COVID-19 task force that it says is regularly updating its pandemic response plan based on guidance from local, state and federal authorities, according to Michael Cook, a spokesman for the bureau.

Cook expressed confidence that the bureau will be able to handle the outreach efforts, and that it's met its goal of 2.67 million applications for the half a million census workers it intends to hire.

Potential for undercounting

Demographers and census experts still see big problems on the horizon.

"The Census Bureau has taken baby steps in terms of delaying things by a couple of weeks here and there, but given the progression of this disease, more strong measures are absolutely needed," said Rob Santos, Vice President and Chief Methodologist of the Urban Institute.

Particularly problematic will be conducting in-person counts in minority communities as well as of students on college campuses, seniors in assisted living facilities and people experiencing homelessness. Not only are these groups at high risk for infection, they're also among those most in need of in-person outreach. With many senior facilities on lockdown and college students being told to move out , an accurate count may become increasingly difficult, despite adjustments the Census Bureau has made to its counting operations.

"There will be potential massive undercounts I believe," Santos said. "With all these basic human needs issues arising, the last thing on anybody's mind is going to be, 'Oh how do we fill out a census form?'"

An inaccurate census could have serious consequences for years to come. Census data is used to determine the number of seats each state has in the US House of Representatives and how much federal funding local communities receive for programs such as highway construction and housing development grants.

By law , the Census Bureau has until December to send final counts to the President and Congress, but the clock is ticking as in-person outreach to those who are unresponsive occurs nationwide from April through July.

On Sunday, the Census Bureau reported that more than 5 million people had responded online to the 2020 Census. While the plan is to finish collecting data by July 31, that date "can and will be adjusted if necessary as the situation evolves in order to achieve a complete and accurate count," according to a March 15 press release

Direct outreach to people experiencing homelessness is still scheduled to start March 30.

Congressional concerns

Lawmakers have started to voice concern. On March 12, when the first initial census invitations were sent out, House Democrats sent a letter to Commerce Secretary Wilbur Ross asking for information on its contingency plans for the 2020 census. On March 3, several Democratic senators sent a letter to the director of the Census Bureau urging him to put a plan in place to deal with coronavirus and protect census workers.

"We particularly want to know what contingency plans are when we get to the face to face interview part of the census," said Minnesota Democratic Sen. Tina Smith, one of the letter's authors. "We know that the risk of being undercounted disproportionately falls on communities of color and low income communities and Native American communities."

Last week, Ross downplayed concerns that the 2020 Census would be impacted by the outbreak of coronavirus, saying that his department is ready to be flexible on how it goes about collecting the new demographics.

"We'll just have to play it by ear," Ross told the Senate appropriations subcommittee. While he didn't provide any details on contingency planning, he noted that the Commerce Department has "done as much as we can to be ready for whatever contingency comes up."

Local outreach

One temporary census worker in California who spoke to CNN on the condition that we not use his name told CNN last week that he was concerned he hadn't been given enough guidance about coronavirus, adding that a supervisor brushed off his concerns when he asked about it.

"It just seems like there should be some strategy or some kind of plan for how to best protect the temporary workers, and how to best protect the public when these canvassers are out interacting with them," he said. "I didn't get a satisfactory answer."

Days later, the worker told CNN he was feeling better after getting new internal guidance from his supervisors about modifications to census procedures resulting in reduced interactions with the public.

"It lessens contact with the general population, eliminates contact with more vulnerable populations, and is consistent with the guidance coming from the CDC and NIH," he said.

In Santa Clara county, which has the most coronavirus cases in California, the manager for the county's Office of the Census, Nicholas Kuwada, told CNN they have begun to make changes to outreach efforts following the spike in confirmed coronavirus cases.

"Currently, we have called off all large gatherings for the census (1,000 people or more) and have begun brainstorming with our partners on alternate activities we can pursue that will comport with the health and safety guidelines as outlined by our County health office," Kuwada said.

Census timeline

A person holds census information at an event where U.S. Rep. Alexandria Ocasio-Cortez (D-NY) spoke at a Census Town Hall at the Louis Armstrong Middle School in Queens, New York City, U.S., February 22, 2020.

The US Census Bureau made a soft launch of its 2020 Census website on March 9, making its form available online. Last Thursday, the Census Bureau began mailing out notices. These initial census invitations ask households to respond online, by phone or by mail.

In mid-April, households that have not responded will receive reminders in the mail, along with a paper questionnaire. From May through July, census takers will visit households that still haven't responded to the 2020 Census online, by phone or by mail. If schools continue to close and widespread quarantines become more likely, the Census Bureau will shift its strategy, said Cook, the Census spokesman.

"Let's say there is this complete community which is on quarantine and people shouldn't be going door to door -- then we are going to alter our planning and implement some social distancing to allow us to send more reminders through the mail to people, more questionnaires," Cook said.

Shifting priorities

Representatives from a number of Census Information Centers tell CNN they are relying on multimedia and television ads to encourage participation in the census while sending out notices regarding coronavirus to the communities they serve. But as coronavirus disrupts people's daily lives, there is growing concern those efforts won't be effective.

"There are people in LA in particular that do not have computers and if they do have computers they don't have the broadband to complete it," said Lydia Camarillo, president of the William C. Velasquez Institute, a Census Information Center based in Los Angeles. "Right now, people are not going to be concerned with filling out the census."

In New York, internet access points were established for historically undercounted communities that may not have internet access. But Meeta Anand, a Census 2020 senior fellow at New York Immigration Coalition, worries that will no longer be an option, especially as areas harder hit by the coronavirus impose curfews.

In Seattle, libraries and community centers had been designated as locations where those without computer access could complete the census. However, the Seattle Mayor's office announced libraries and community centers would be closed until April 13.

Anand said the New York Counts 2020 initiative that the Coalition facilitates has not received any guidance from the Census Bureau beyond what they've put out online.

"We'd love to see the Census Bureau pushing back the start of their door knocking," Anand said, "just to give us an extra month to do the outreach that's going to naturally slow down during this time."

This story has been updated with comments from a census worker.