WASHINGTON (CNN) -- Sen. Larry Craig filed an appeal Monday in his continued legal fight stemming from a bathroom sex sting this summer.
Sen. Larry Craig, R-Idaho, initially said he would resign at the end of September but then changed his mind.
The Idaho Republican wants the Minnesota Court of Appeals to overturn a judge's decision refusing to let him withdraw a guilty plea to misdemeanor charges stemming from his arrest in June.
"From the outset Senator Craig has maintained that he is innocent of any illegal conduct at the Minneapolis airport," Craig's lawyer, Billy Martin, said in a written statement. "Like every other citizen, Senator Craig has the constitutional right to make every effort to clear his name."
Martin called the judge's decision "a manifest injustice."
In an interview Sunday with Boise, Idaho, TV station KTVB, Craig said "we don't know what the appellate court will say to me," according to the station's Web site. Watch Craig discuss his chances on the appeal »
"Honestly, the appeals courts tend to defend the courts below them. It is my right to do what I'm doing. I've already provided for Idaho [the] certainty that Idaho needed, I'm not running for re-election. I'm no longer in the way. I am pursuing my constitutional rights."
The appeals process could take months to complete, court spokesman Kyle Christopherson said.
Craig entered a guilty plea after his arrest in a men's room at the Minneapolis-St. Paul International Airport for allegedly propositioning a plainclothes police officer for sex.
Craig originally said he would resign from the Senate on September 30 if he could not get the guilty plea withdrawn. He later postponed his decision until the judge ruled.
After an October 4 ruling against him, Craig changed course, saying he would not resign and would continue to pursue his legal options.
"I am innocent of the charges against me," he said at the time.
The Idaho lawmaker's decision not to resign has created a political headache for the Senate's Republican leadership.
When news of the arrest first surfaced, GOP leaders called for an investigation by the Senate Ethics Committee. They later applauded Craig's decision to resign.
And when Craig announced that he would continue to serve in the Senate, GOP leaders did not appear pleased.
"It's embarrassing for the Senate. It's embarrassing for our party," said Sen. John Ensign of Nevada, who leads the GOP's Senate campaign committee, on the day of the judge's decision. "I think it's best for the U.S. Senate, it's best for certainly his party, that he just keeps his word."
In an interview taped Sunday with NBC's Matt Lauer, Craig complained that GOP presidential candidate Mitt Romney "threw me under the campaign bus" when news of his arrest came out.
"He not only threw me under his campaign bus, he backed up and ran over me again," Craig told Lauer in the interview set to run Tuesday night, according to MSNBC.com.
Romney, former governor of Massachusetts, called Craig's behavior "disgraceful" and urged the senator to resign when news of the arrest broke in August.
Craig was Romney's Senate liaison before resigning from the campaign.
Romney spokesman Kevin Madden defended the presidential candidate's response. "Gov. Romney simply believes that a public office is a public trust," Madden said. "He believes when a public official enters a guilty plea, they have broken that public trust and should step aside for the sake of their constituents."
Also in the Lauer interview, Craig and his wife, Suzanne, denied that their marriage is a cover for his homosexuality, according to MSNBC.com.
"People know me and know that I would never do that," said Suzanne Craig, MSNBC.com reported. "That's almost like selling your soul for something."
The senator has denied he is gay. "I love this woman very, very much," Larry Craig said, according to MSNBC.com. "The day I found her, I fell deeply in love. And we're heading toward our 25th anniversary."
When she learned the story was going to break, Suzanne Craig said, "I felt like the floor was falling out from under me. ... And I felt like almost like I was going down a drain for a few moments," according to MSNBC.com. E-mail to a friend
CNN's Scott Anderson and Alexander Romney contributed to this report.