If an action or a decision opens the floodgates, it allows something to happen a lot or allows many people to do something that was not previously allowed: Officials are worried that allowing these refugees into the country will open the floodgates to thousands more.

What does it mean when flood gates are open?

: to remove something serving to restrain an outburst Many people fear that the court's latest ruling will open the floodgates for/to a host of new lawsuits.

Is open the floodgates an idiom?

Idiom: 'Open the floodgates'