Congress’s watchdog said the Census Bureau has a plan, should the Supreme Court order a citizenship question deleted from written and online forms to be used in 2020, but it’s not clear how the plan would be carried out.

The report from the Government Accountability Office focused on a handful of risks to the 2020 Census.

A key remaining question is whether the Census will ask if people are U.S. citizens.

Congress’s watchdog found that the Census Bureau has talked about what to do if the Supreme Court orders the citizenship question removed less than a year before counting starts. But the report said those steps have not been added to a broader plan for what to do if there are late changes to the Census form.

Advocates have said a citizenship question will stoke fear among immigrants and cause an undercount.

Phoenix officials have said the city’s noncitizen population is worth more than $1 billion in funding over the next decade.