President Biden is planning executive action that would allow him to shut down the US-Mexico border once the number of migrant crossings reaches 4,000 per day, a source close to the White House told The Post Wednesday.

The order would match a provision in the bipartisan border bill that failed to pass the Senate in February, which gave the president authority to expel migrants when border crossings reached the same daily average.

The legislative proposal would have given the homeland security secretary discretionary authority to carry out removals — but would have made deportations mandatory when illegal entries surpassed 5,000 per day over a one-week period.