PORTLAND, Maine — Maine Sen. Susan Collins says she’s going to vote against President Barack Obama’s nominee for treasury secretary.

Collins, a Republican, says Timothy Geithner’s professional background and experience should inspire confidence. But she says they are “overshadowed” by personal issues regarding his tax returns.

She said Monday that Geithner’s tax return problems are not a matter of “careless mistakes” as he described them. Instead, she describes it as “inexcusable negligence.”

Maine’s senior senator, fellow Republican Olympia Snowe, voted in favor of Geithner’s confirmation last week on the Finance Committee.