941 - tax liability deposit threshold

if the tax liability for a quarter is less than $2,500, it may be paid with the quarterly filing of Form 941. If it is $2,500 or more, then it must be deposited on either a monthly or semi-monthly basis.
The IRS will notify you each November as to whether you are a monthly or semi-monthly depositor. The IRS uses a 1 year look back period ending the preceding June 30th.