Consumers relying more on their MasterCard for credit and debit purchases helped the second largest payments processor see a net income of $514 million, or $4.03 a share, in the fourth quarter of 2011 – that’s a 23.7 percent jump in profit over a year ago.

Visa and MasterCard have agreed to allow merchants to encourage customers to use lower cost credit or debit cards — and potentially provide rebates or discounts for doing so — under a settlement with the U.S. Justice Department announced today. Simultaneously, Justice officials said that an antitrust lawsuit would proceed against a third payment network, American Express, challenging rules that prevent merchants from offering consumers “any cost saving options, such as discounts or rewards, for using less expensive forms of payment.”

Bolstered by jumps in international credit and debit transactions, MasterCard posted a second quarter earnings increase of 31 percent. The No. 2 payments processor said today that net income climbed to $458 million, or $3.49 per share, from $349 million, or $2.67 a share, a year ago.