Because parental leave is a popular benefit, particularly among millennial employees, and it is likely more companies will offer the benefit to employees, credit unions may want to review their current policies to check for any discriminatory pitfalls that can lead to costly legal issues.

The $3.7 billion Bellco Credit Union wasn't so lucky.

In March, the Denver Metro Fair Housing Center claimed that the Greenwood Village, Colo.-based credit union discriminated against women by denying them mortgages because they were on maternity leave, according to a federal lawsuit filed in U.S. District Court in Denver. Bellco has vehemently denied the state and federal allegations of discriminatory lending practices.

"To our knowledge, no one ever applied for, nor was denied a home loan based on the call recordings from the Denver Metro Fair Housing Center," Bellco said in a prepared statement. "We believe the allegations in the suit could have been addressed between our two not-for-profit companies directly instead of through a lawsuit where valuable resources are being spent on attorneys and court costs. Our attorneys are investigating the specific allegations in the complaint and will respond to them in court, but we are confident that the lawsuit has no merit."

And in 2014, the $6.4 billion Mountain America Credit Union in West Jordan, Utah agreed to pay $25,000 to settle allegations that it discriminated against prospective borrowers on maternity leave.

MACU generally denied that it discriminated against borrowers on maternity leave and said that the offending policies against borrowers on maternity leave came from CMG Mortgage Insurance Co., a mortgage insurance company that the credit union used to process certain mortgages.

However, the HUD investigation found evidence that MACU's procedures and policies regarding borrowers on maternity, paternity or pregnancy constituted "alleged discriminatory practices that may have been pervasive or institutional in nature."

Since 2010, HUD has received almost 150 complaints alleging maternity-leave discrimination against lenders across the nation and has obtained more than $8 million in settlement compensation for victims.

In addition to the HUD cases, the U.S. Justice Department has also been pursuing lenders who discriminate against moms on maternity leave, according to a report in the Los Angeles Times. Both federal agencies have settled and imposed hefty monetary penalties against Bank of America, PNC Mortgage, Wells Fargo, Citizens Bank, Cornerstone Mortgage Company and giant credit union and bank mortgage insurer MGIC. The MGIC settlement reportedly involved 70 women, established a compensation fund of more than $500,000 for alleged discrimination victims and a $38,750 civil penalty.

Alexia Smokler, a former program analyst for HUD's office of fair housing and equal opportunity, believes the maternity leave discrimination issues initially surfaced after the 2008 mortgage meltdown when financial institutions substantially tighten credit standards for mortgage applicants.

But the issue captured national exposure when the New York Times reported in 2010 that mortgage lenders were allegedly denying credit to qualified borrowers because of pregnancy or maternity leave.

The article highlighted Dr. Elizabeth Budde, a Seattle-area oncologist, who had been approved for a mortgage but the lender reportedly revoked its loan approval after learning she was on maternity leave. Even though the physician was receiving full pay and benefits while she cared for her baby, the lender said it could not consider her income because she wasn't working.

The article led to the launch of multiple investigations by HUD.

Although lenders have every right to determine the incomes of families, they may not single out women on maternity leave for special guarantees, ignore their other financial resources or assume they will not return to work, Smokler said.

Other financial resources that a borrower on unpaid maternity leave may have to make mortgage payments and the assumption that the borrower won't return to work are key accusations in the Bellco case.

The Denver Metro Fair Housing Center said it conducted telephonic testing of several banks in the area to determine if any were discriminating against women on maternity leave.

Testing revealed that Bellco allegedly maintains a discriminatory policy of denying home mortgage loans to women on maternity leave, requiring women return to work for at least 30 days before the credit union would even consider their home mortgage loan application, according to conversations that the DMFHC's telephone testers had with Bellco loan officers. This allegedly was the credit union's policy regardless of whether the leave was paid or unpaid and regardless of whether the women had savings to compensate for any temporary salary reduction resulting from the maternity leave, the lawsuit claimed.

In one example, the fourth tester reminded the Bellco loan officer that she was on paid maternity leave.

"He [the loan officer] responded that Bellco still would not consider her earnings until she had returned to work for a month because '[a] lot of people say they are going to go back to work and then they don't so that is why we require that you actually are back at work in order to use your income,'" according to the lawsuit.

According to HUD, when lenders make decisions assuming mothers won't return to work, it's not only illegal but also an unreasonable assumption because rejecting home loans for women on maternity leave could result in excluding huge number of American families from the mortgage market.

"Mostly, people return to work because they need the dual income," Brian Sullivan, a HUD supervisory public affairs specialist, said.

The labor participation rates among women with children bear that out.

The labor force participation rate for mothers with children under six years old was nearly 65% and the labor force participation rate for mothers with children six to 17 years old was 75% in 2016.