Came across a useful script for an age old problem in SharePoint. May work on versions beyond 2013, but haven’t tested. Posting here for future reference (Found here:

$WebAppURL =""
#Get a collection of all websites
$WebsColl = Get-SPWebApplication $WebAppURL | Get-SPSite -Limit All | Get-SPWeb -Limit All
ForEach ($web in $WebsColl)
    # Only run this if access requests are currently enabled AND if the website does NOT inherit permissions
    if($web.RequestAccessEnabled -and $web.Permissions.Inherited -eq $false)
        # Disable access request
        $web.RequestAccessEmail = ""
        write-host "Access request disabled for website: " $web.URL