LITTLE ROCK, Ark. (AP) - Arkansas' state treasurer resigned Tuesday after being accused of taking at least $36,000 in cash - sometimes stashed in a pie box - from a broker who later came to manage a large share of the state's $3.3 billion investment portfolio.

Democrat Martha Shoffner held the office since 2007 and was re-elected in 2010. She was barred by term limits from seeking re-election next year.

"I am proud to have been elected by and to have served the people of the state of Arkansas and regret that I can no longer perform the duties and responsibilities owed to the public," Shoffner wrote in a letter to Gov. Mike Beebe. Shoffner's resignation was effective 5 p.m. Tuesday.

Shoffner's attorney provided a copy of the letter. Beebe's office did not immediately return a call late Tuesday.

She was under pressure from both Democrats and Republicans to step down after the FBI arrested her Saturday in a sting operation. She spent the weekend in Pulaski County Jail and made her initial court appearance Monday. She didn't enter a plea, but her attorney, Chuck Banks, said she would plead not guilty at the appropriate time.

Shoffner, 68, was released on her own recognizance but ordered to surrender her passport. A federal grand jury will decide whether to indict her. She's charged with attempt and conspiracy to commit extortion under color of official right.

The charges carry maximum penalties of 20 years in prison and up to a $250,000 fine. A next court date was not set.

"It would be very hard, in my opinion, for that office to properly function under her continued leadership," Beebe, a Democrat who was among those calling for Shoffner to resign, said Monday.

Beebe earlier Tuesday said he'd consider asking lawmakers to remove Shoffner if she didn't resign. The top Republican in the House urged Beebe to convene lawmakers to begin removing her.

Federal prosecutors allege Shoffner accepted $12,000 a year from a broker who would sometimes deliver cash in a pie box, with the pie included. They said the broker is cooperating with investigators.

An FBI affidavit filed in federal court alleges that a broker - unidentified in court documents - would roll up cash in $6,000 increments and have it delivered to Shoffner's office every six months. At least two of the payments were delivered in a pie box with a pie. The broker "recognized his/her bond business with the state grew because of the payments," the affidavit said.

The payments were made after Shoffner asked the broker for $1,000 a month to pay her rent in Little Rock, according to the affidavit. The document said the broker was granted immunity in exchange for his or her cooperation.

Legislative auditors last year questioned Shoffner's selling of bonds before they matured, a practice that they said cost the state more than $434,000 worth of earnings.

Shoffner was arrested at her home in Newport after the broker agreed to record the meeting and bring $6,000 in a pie box, according to the affidavit. FBI agents executed a search warrant and found the cash inside a cigarette package in Shoffner's kitchen. Shoffner admitted that she accepted the payments from the broker, the FBI said in its affidavit.

After Monday's court appearance, Shoffner told reporters she didn't plan on stepping down. But her attorney said he would probably advise her to resign.

Lawmakers could have held impeachment proceedings to remove Shoffner from office if she didn't resign, but legislative leaders stopped short of saying they'd seek that option.

Attorney General Dustin McDaniel and U.S. Sen. Mark Pryor also had called for her resignation in the wake of the charges. So had the heads of the state Democratic and Republican parties.

Whoever Beebe appoints to fill Shoffner's term cannot run for the seat next year.

Shoffner is a former state representative who was first elected treasurer in 2006 and won a second term in 2010 after defeating a Green Party challenger.

During her re-election bid, she apologized for referring to the state trooper driving Beebe as a "manservant." Shoffner made the comments while defending her personal use of a state vehicle.