The US Department of Justice has ordered states to expand how they report undocumented immigrants to the federal government, according to a legal opinion from Tuesday that reverses a policy that has been in place for nearly 30 years.

Under the new opinion, issued by the department’s office of legal counsel, any state that takes federal money through support schemes for low-income Americans, including Temporary Assistance for Needy Families (TANF) or Supplemental Security Income (SSI), must now report undocumented immigrants across its entire state government, not just through the specific welfare office that runs the program.

TANF and SSI are two of the country’s largest programs helping low-income families, and elderly and disabled residents.

The opinion withdraws a 1998 interpretation issued during the Clinton administration, which had confined the reporting requirement to the state agency directly responsible for administering the federal program in question.

Deputy assistant attorney general Joshua Craddock, who authored the new opinion, wrote that the earlier interpretation was based on flawed legal reasoning. “We are forced to conclude that our prior opinion erred in its analysis and result,” he wrote.

Craddock also dismissed the argument that Congress’s decades of inaction on the issue amounted to implicit endorsement of the narrower reading. “The fact that subsequent congresses have not affirmatively corrected the 1998 Opinion’s interpretation of section 404 does not alter the plain meaning of the statute,” he wrote.

Assistant attorney general T Elliot Gaiser defended the reinterpretation in a statement. “When a state chooses to participate in TANF, it accepts the obligation to report illegal aliens in the United States,” he said. “Tax dollars intended to help vulnerable Americans should not perversely encourage illegal entry into the United States, but rather should reinforce our laws and our borders.”

The new policy will not be applied retroactively. Craddock wrote that it “cannot retroactively alter agreements” made under the prior interpretation, since “the parties to those agreements had different understandings of states’ reporting obligations.” US states that object to the new requirement, he wrote, remain free to withdraw from the programs.

The opinion also addresses when a state can be said to “know” someone is undocumented. A 2,000 federal regulation had required a formal legal finding, confirmed by immigration authorities, before that standard was met.

Craddock said that bar was too high. An agency cannot avoid the obligation, he wrote in a footnote, “by deliberately refusing to consider readily available information or by insisting on a formal adjudication that the statute nowhere requires”.