WASHINGTON — The Supreme Court on Wednesday unanimously upheld an Arizona state legislative map drawn by an independent redistricting commission, rejecting a challenge from Republicans who said the map was too favorable to Democrats.

The court last year upheld the commission’s role in drawing congressional maps, ruling that Arizona’s voters were entitled to try to make the process of drawing district lines less partisan by creating an independent redistricting commission.

Wednesday’s decision in Harris v. Arizona Independent Redistricting Commission, No 14-232, concerned a challenge from voters who said the state map the commission drew after the 2010 census violated the principle of “one person one vote” and was infected by unconstitutional partisanship.

The challengers noted that there were variations in the districts’ populations. But Justice Stephen G. Breyer, writing for the court, said the contested deviations were less than the 10 percent that the Supreme Court has said is generally constitutionally tolerable.