The U.S. Treasury Department is getting out of the last piece of its investment in M&T Bank Corp.

Treasury on Monday launched a secondary public offering of 1,218,522 warrants it held that gave it the right to buy shares of M&T.

Under the “modified Dutch auction” format, potential bidders can place bids at any price, in increments of 25 cents, at or above the minimum bid of $23.50 per warrant. The auction, conducted by Deutsche Bank Securities as the sole “book-running manager,” began at 8 a.m. and concluded at 6:30 p.m.

The 10-year warrants were granted to the federal government in December 2008 by Buffalo-based M&T as part of Treasury’s $600 million preferred stock investment in the bank under the Troubled Assets Relief Program, or TARP.

M&T, which also inherited $151.5 million and $330 million in TARP money from its purchases of Baltimore-based Provident Bankshares Corp. and Delaware’s Wilmington Trust Corp., later repaid $700 million of the $1.08 billion in total TARP money and Treasury last summer auctioned the remaining $381.5 million directly to private investors, leaving just the warrants.

However, M&T has already been free of the terms and restrictions of the TARP program since last summer, so the auction of the warrants has no effect on the bank, spokesman C. Michael Zabel said.

The warrants, which still have six years remaining, give the holder the option to purchase M&T shares at a fixed price of just over $73 per share. M&T stock was trading at $97.93 on Tuesday.

Treasury said proceeds of the sale will provide an additional return to taxpayers beyond the dividends the government already received on the preferred stock.