Mayor R.T. Rybak warned voters Friday about last-minute political attacks they may witness before heading to the polls Tuesday to elect his successor.

In a post on his Tumblr page, Rybak instructed readers to be skeptical about critical mail pieces.

"Look to the bottom of the piece for the disclaimer, meaning who paid for it," Rybak wrote. "If it doesn’t have a candidate’s name on it, ask more questions."

He specifically highlighted the firefighter's union, which he said is known for its "bombastic attack literature."

"I saw a piece in the 13th Ward that misleadingly attacked me while encouraging a vote for a Council candidate," Rybak wrote. "Bluntly: if it comes in the last week of a campaign, be very skeptical of anything you hear from the fire union and their leader, who is known for being over the top and not always accurate."

That refers to union president Mark Lakosky, who is frequently quoted in the media criticizing Rybak and budget chair Betsy Hodges for staffing cuts. The union has endorsed Mark Andrew. Lakosky said Friday night he has consistently used the city's own data on staffing, response times and numbers of fire and medical responses, and that he is simply being "passionate" about restoring staff cuts.

Rybak added that he has "tremendous respect for the professionals in the Fire Department who protect us every day. They are heroes."

The mayor also encouraged people to read a Friday Star Tribune story about some of the money pouring into the mayor's race.

"Getting a contribution from someone does not mean they can “buy you,” but it is important for voters to know who will have influence and who is putting lots of money into this campaign," he wrote.