American Express announced Thursday plans to suspend its share buyback program, citing additional charges incurred from tax reform.

"The upfront charge triggered by the Tax Act reduced our capital ratios and, as a result, while we will be continuing our quarterly dividends at the current level, we plan to suspend our share buyback program for the first half of 2018 in order to rebuild our capital," CEO Kenneth Chenault said in a statement.

The credit card company estimated those upfront charges would cost about $2.6 billion, and estimated the tax rate under President Donald Trump's "Tax Cuts and Jobs Act" would come to about 22 percent before discrete tax items.

American Express also said it planned to invest $200 million more toward customer growth initiatives in 2018 than originally anticipated, and announced it had made an incremental contribution toward employee profit-sharing plans. The company did not disclose how much.