President Obama announced on Thursday that he's taking on the country's biggest banks.

On top of the financial regulatory overhaul he already seeks, the president is proposing to Congress tough new restrictions on big banks.

His regulations would limit the size of large financial institutions. The new rules would also limit a bank's ability to engage in high-risk trades.

"We cannot accept a system in which shareholders make money on these operations if the bank wins but taxpayers foot the bill if the bank loses," Obama said at a newsconference.

Critics argue the move would cut bank profits and make them less likely to lend. Stock markets around the world have dropped, echoing that fear.