In the 2018 proposed budget the Census would be allocated $1.52 billion, up $50m from 2017. This includes $276m for salaries and expenses/current surveys and programmes and $1.25bn for periodic censuses and programmes (which covers the American Community Survey and 2020 Census).

But the Insights Association said initial estimates suggest more than $1.8bn will be needed in 2018 to properly prepare for the Census, in particular with its 2018 end-to-end test run and improved IT infrastructure.

It said a $300m increase was needed, rather than the $50m allocated.

Howard Fienberg, director of government affairs for the Insights Association, said: "When you're trying to balance the federal budget you have to carefully prioritise. The White House appears to have avoided doing so, neglecting a Constitutionally-required function of government in the process.

"The FY18 funding request for the Census Bureau is woefully inadequate. Increased funding is necessary to prepare for a modern Census with technological innovation. Under-funding the Census in FY18 puts us on a potential collision course with massive emergency appropriations to try to get the decennial headcount done accurately and on time."

He said he was particularly concerned Congress might divert funding from the American Community Survey (ACS) but that if the sample size was decreased the accuracy of the data would diminish.