The US Supreme Court upheld a key provision of a controversial state immigration law in the first of this week’s landmark rulings likely to influence the debate before November’s presidential election.

The court ruled that Arizona police are constitutionally allowed to request documents from anyone they suspect of being in the US illegally. But it overturned three of the other key provisions targeting illegal immigrants, agreeing with the Obama administration that the federal government has jurisdiction over immigration matters.

The decision will ensure the question of how to deal with illegal immigrants remains near the top of the political agenda in the lead-up to the November elections, together with the administration’s healthcare reforms, on which the court is expected to rule this Thursday.