WASHINGTON — Every weekend, Cindy Martinson treks from her home in Mason City, Iowa, about 160 miles roundtrip to Waseca. She visits the federal prison there, where her daughter Mandy Martinson, a first-time offender, is in the middle of a 15-year prison sentence.

Cindy Martinson knows her daughter made mistakes and broke the law. Mandy Martinson was at a low point in her life, her mother said, addicted to methamphetamine when she allowed a drug dealer she was dating to move in with her. Within weeks, police raided her house.

“She hurt herself and her family. And she knows that. But it is just not fair,” Cindy Martinson, 64, said. “It’s got to change not just for her. Everything is so overcrowded and it is just wrong.”

Concerns about both the fairness and the costs of cases like Mandy Martinson’s have been growing in Congress, and the issue is gaining new speed as an unusual coalition of Tea Party conservatives and liberal Democrats push for the largest overhaul of federal sentencing guidelines yet.

The Senate Judiciary Committee will hold a hearing this week on minimum sentences. The committee is considering two bills, each sponsored by a liberal Democrat and a Tea Party Republican, that would allow judges to waive mandatory minimum sentences in many circumstances, particularly for some drug crimes. Wednesday’s hearing is the first step in legislation that advocates and lawmakers in both parties say stands a chance of winning enactment by the end of the year.

Attorney General Eric Holder has shown interest in working with Congress to make permanent changes in sentencing laws. Holder last month instructed federal prosecutors to stop charging nonviolent drug offenders with crimes that carry mandatory minimum sentences.

Sentencing reform lands in an area of rare common ground between liberals and conservatives. Just a few years ago, it was an issue shunned by many politicians in both parties, lest they be labeled soft on crime.

Now it’s made unlikely teammates of Tea Party libertarian Sen. Rand Paul, R-Ky., and Judiciary Committee Chairman Patrick Leahy, a liberal Vermont Democrat. They’re co-sponsoring one of the two sentencing bills now before the committee. Co-sponsoring the other one are Sens. Mike Lee, R-Utah, another conservative championed by the Tea Party, and the Senate’s No. 2 Democrat, liberal Sen. Richard Durbin of Illinois.

The four senators make similar cases for sentencing reform: Many of the sentences are unfair, prisons are overcrowded with nonviolent drug offenders, and it’s costing taxpayers too much money.

Prison costs have ballooned in the past 30 years, with the Bureau of Prisons budget now around $6.8 billion, or about 25 percent of the Justice Department’s total. The yearly cost of housing a federal prisoner ranges from $21,000 to $33,000, depending on the prison’s level of security, and is steadily rising.

The United States has the largest prison population in the world with more than 1.5 million prisoners in 2012, according to the Bureau of Justice Statistics, including more than 218,000 federal prisoners. About half of federal prisoners are drug offenders, nearly all of whom faced some form of mandatory minimum sentencing. They include Mandy Martinson.

Police raided her house in Mason City in January 2004. She was 27 at the time. They found 10 pounds of marijuana, two pounds of high-purity methamphetamine known as “ice” and two guns, components of a northern Iowa drug ring run by her then-boyfriend, whom court documents identify as Justin Dana.

Cindy Martinson said her daughter knew Dana was a drug dealer, but she was a drug addict and under Dana’s control.

A local judge released Mandy Martinson on her own recognizance after her arrest and she eventually sobered up and resumed a job as a dental hygienist for several months.

But at trial, it became clear Mandy Martinson would serve a long sentence, Cindy Martinson said. Dana testified against his girlfriend, saying she performed menial tasks, like counting money, helping his drug operation. He also testified one of the guns found in the raid belonged to him but said Mandy sometimes carried it.

Like the local judge, the federal judge, James E. Gritzner, acknowledged that Martinson posed little threat. But Gritzner said his hands were tied by sentencing guidelines.

He sentenced Mandy Martinson to 15 years in prison for drug and weapons charges. She had never been arrested for anything prior to that. Now 35, Martinson’s term is three years longer than Dana’s because he agreed to testify against her and others.

Julie Stewart, the president of Families Against Mandatory Minimums, said prisons are filled with inmates like Martinson. A former staffer at the libertarian Cato Institute, Stewart made sentencing reform her cause after her brother was arrested for growing marijuana and sentenced to a long mandatory sentence.

She said this is the most momentum she’s seen behind efforts to change sentencing laws.

“Let’s put it this way: I’ve been doing this for 22 years and this is the first time since 1993 I have felt significant attention from Congress on this issue,” she said.

“There’s a new era of bipartisanship on this issue,” said Rep. Jason Chaffetz, another champion of conservative groups and a leader on the issue in the Republican-held House.

Chaffetz, R-Utah, introduced a bill in the House that is co-sponsored by several Democrats. It would put in place a post-sentencing “risk assessment system” allowing some prisoners to earn credits toward different living arrangements, such as a halfway house or house arrest.

“There are smarter, cheaper ways to deal with this than what we’ve been doing,” he said. “And we have no choice,” because of costs.

Leahy and Paul’s bill in the Senate would expand a “safety valve” provision, which currently allows a small number of low-level federal drug offenders to avoid mandatory minimum penalties, to all federal crimes with mandatory minimum sentences if certain conditions were met.

Durbin and Lee’s bill would expand the “safety valve” to more drug offenses, but not all federal crimes with mandatory minimum sentences.