San Francisco and Santa Clara counties filed a lawsuit Tuesday challenging a Trump administration move to penalize immigrants who use or are likely to use public benefit programs such as food stamps, housing assistance or Medicaid.

Why it matters: Per Axios' Stef Knight, the rule would make it much harder for immigrants with low incomes or low levels of education to obtain visas or green cards. And it would be much harder for immigrants already in the U.S. to stay longer, change their immigration status or become citizens if they have used any of the specified safety net programs.

The big picture: The suit, filed in the U.S District Court of Northern California, is the first legal challenge to the so-called "public charge" rule, unveiled in its final form on Monday, the Mercury News notes. The rules are due to come into effect in mid-October.

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