The IRS has recently issued revenue bulletin No. 2015-36 that states that they will no longer accept checks that are greater than $999,999,999.00. This new check policy is set to be implemented on January 1, 2016. The reason behind the new policy has to do with avoiding mistakes because the check processing equipment that the IRS has cannot process checks that are over $1 million. Checks over that amount have to be manually processed by hand and that can lead to mistakes. So far no limits have been placed on credit card payments, though any client wishing to pay that way might want to check with their credit card company.
See Kelly Philips Erb, IRS To Refuse Checks Greater Than $100 Million Beginning In 2016, Forbes, September 8, 2015.
