The US supreme court appeared poised on Monday to curtail how mail-in ballots can be counted if they arrive after election day, which would affect laws in more than a dozen states during a midterm election year.

The justices are considering Watson v Republican National Committee, a challenge over a Mississippi state law that was brought in 2024 by the Republican party. Mississippi allows mailed ballots to be counted if they arrive within five business days of election day, so long as they were postmarked by election day. Mississippi changed its laws in 2020, during the Covid-19 pandemic.

Fourteen states, Washington DC and three US territories have similar laws that allow for late-arriving ballots to be counted. Based on the justices’ questions, it is clear the case is not focused narrowly on Mississippi’s grace period, but on other states’ rules, which in some cases allow for a longer grace period and don’t require postmarks.

Mississippi, a red state, is defending its ability to set its own procedures for elections against the challenge from the Republican party, which argues that the grace period violates federal laws that set election day for the first Tuesday of November.

I realise that The Guardian is likely only tangentially aware of the actual requirement, which is “the first Tuesday after the first Monday in November” to avoid holding elections on All Saints’ Day.