WASHINGTONWASHINGTON (Reuters) - The Supreme Court on Friday blocked lower court rulings ordering Republican legislators in Michigan and Ohio to redraw U.S. congressional maps ahead of the 2020 elections, dealing a blow to Democrats who had argued that the electoral districts were intended to unlawfully diminish their political clout.

The justices granted requests from Republican lawmakers in both states to put those decisions on hold, halting further action in the cases and the need to rework electoral district boundaries. The justices did not provide any explanation for their brief orders.

The lower courts found that the electoral maps in the two states had been drawn to entrench Republicans in power by manipulating boundaries in a way that reduced the voting clout of Democrats - a practice known as partisan gerrymandering - in violation of the U.S. Constitution.

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While both disputes involve U.S. House of Representatives districts in the two states, the Michigan case challenges districts in the state legislature as well.

The decisions in Michigan and Ohio that were put on hold by the justices were the latest rulings by federal courts determining that electoral maps designed by a state's majority party unconstitutionally undermined the rights of voters who tend to support the other party.

But the action by the justices was not unexpected as they weigh two other gerrymandering cases - one from North Carolina and the other from Maryland - that could decide definitively whether federal judges have the power to intervene to curb partisan gerrymandering. The rulings in those cases, due by the end of June, are likely to dictate whether the legal challenges against the Ohio and Michigan electoral maps can move forward.

In the North Carolina case, Republican legislators were accused of rigging congressional maps to boost their party's chances. In the Maryland, Democratic lawmakers faced similar allegations over one U.S. House district.

The Ohio and Michigan lawsuits accused Republican-controlled legislatures in the two states of discriminating against Democratic voters for their political views in violation of the U.S. Constitution's guarantees of equal treatment under the law and freedom of association.

Critics have said that gerrymandering, a feature of U.S. politics for generations, has become increasingly extreme and effective at advancing the interests of a political party as a result of precise voter data and powerful computer technology, illegally shaping the outcome of elections.

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The Supreme Court has previously intervened when legislators impermissibly sought to dilute the voting power of racial minorities, but it has never curbed gerrymandering for purely partisan purposes.

The Michigan and Ohio lawsuits were filed by voting rights groups and individual Democratic voters. Nine U.S. House and 25 state legislative districts were at issue in Michigan, while Ohio's case involved 16 U.S. House districts.

A three-judge panel in Detroit on April 25 ruled in the Democratic voters' favor in the Michigan case, calling gerrymandering a "pernicious practice that undermines our democracy," and ordered state officials to draw new maps by Aug. 1.

A three-judge panel in Cincinnati on May 3 sided with the Democratic voters in the Ohio case, and ordered the state to create a plan to fix the map by June 14.

Electoral districts are typically redrawn once a decade after the U.S. census to reflect population changes. In many states, the party in power controls the map-making.