The tweet, which did not appear in Walker's timeline for much of the day but was still visible for hours at its permalink, was a weirdly timed surprise: Walker wasn't supposed to formally announce his candidacy until Monday in Wisconsin.

On Friday, a photo with the words "Scott Walker Is Running For President" was tweeted from Walker's account.

Twitter did not provide further information on what exactly happened.

"We're looking into today's issue, and we've determined the Walker team was not at fault," the spokesman said in a statement.

On Monday, Walker is expected to announce his candidacy, which will be the culmination of a lot of early pre-official campaigning for most of the year.

Since Iowa Freedom Summit this winter, he has aggressively campaigned in early presidential primary states this year and is considered a top Republican contender for the nomination.

The Wisconsin governor is best known for his battles with public unions. After he passed a budget that required public workers to contribute more money to their pension plans and limited collective bargaining in the public sector, unions protested for weeks, and ultimately helped force a recall election in 2013, which Walker won decisively. Because of the recall, the Republican has won three statewide elections in a blue state.

Early on, Walker has focused on his conservative record and pitched himself as a slightly more populist alternative to many of the other prospective candidates.