The U.S. Supreme Court announced Monday it will hear a case that could decide whether states can count postmarked mail ballots that arrive after Election Day — something that about 20 states and territories currently allow.

Mississippi is one of those states, and in June, its top election official asked the court to hear a lawsuit filed by the Republican National Committee that argues the state's mail ballot grace period violates federal law.

An appeals court sided with the RNC. The ruling, which came while voters were casting ballots in last year's presidential election, did not go into effect immediately.

Nearly 20 states plus Guam, Puerto Rico, the Virgin Islands and Washington, D.C. , currently accept and count mail-in ballots that are received after Election Day — typically, onl

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