The couple, who had just had twins, thought everything was on track when their mortgage application was approved and the closing for their new Virginia home was scheduled.

But when the lender — FirstBank — learned that the wife was on maternity leave, it reversed its decision and denied the loan, causing the wife and twins to move in with her parents. There wasn’t enough space, so her husband moved to an apartment with their 3-year-old.

Three-quarters of U.S. moms are in the labor force, but securing a mortgage while on maternity leave or pregnant is “a significant challenge and producing a steady flow of complaints,” said Bryan Greene, HUD’s general deputy assistant secretary for fair housing and equal opportunity.

The U.S. Department of Housing and Urban Development launched 15 maternity-leave discrimination investigations this year, part of a pattern that has seen the federal agency investigate 173 allegations against lenders since 2010, Greene said.

In the latest case, FirstBank Mortgage Partners will pay $35,000 to settle allegations that it violated the Fair Housing Act when it denied a mortgage loan to the couple because the mother was on maternity leave, though she planned on returning to work outside the home.

Both the Justice Department and HUD have settled with — and levied monetary penalties against — a number of lenders, including Bank of America, PNC Mortgage, Cornerstone Mortgage and MGIC. The MGIC settlement in 2012 involved 70 women and led to a $511,250 compensation fund for the alleged discrimination victims and a $38,750 civil penalty.

“In many instances, we find lenders just stop dead at the word ‘pregnancy’ or ‘maternity leave,’ ” Greene said. “And in many instances, women are planning to go back to work, but lenders don’t make those inquires. They go on the assumptions that women won’t return to work.”

The banks, which denied any wrongdoing as part of the settlement, argue that there will be a loss of income during maternity leave and women may not return to work.

That assumption is “antiquated, ridiculous and just not true,” said Kristin Rowe-Finkbeiner, executive director of MomsRising, a national advocacy group with more than 1 million members.

Her organization is working with HUD to combat the practice. The group is asking members to write in if they experience lending discrimination. The reports will then be sent to HUD.

“There’s a myth that moms are not as committed to work as dads,” Rowe-Finkbeiner said. “But, this is not the ‘Mad Men’ era with Betty Draper at home.”

Today, 50 percent of women return to work within three months after giving birth to their first child, she said. More than 70 percent of mothers with young children are in the workforce, and four in 10 mothers are the sole or primary breadwinner.

On the MomsRising Web site, Linda Falcão, a civil rights attorney and mother of three from Pennsylvania who was one of the first people to raise the issue, said a bank told her family to write a “motivational letter.”

“After asking two separate mortgage reps to be excused from this aspect of the process (and being refused) and after telling them I thought it was illegal (they didn’t seem to care) I was inspired to write a satirical letter about what ‘was brewing in my uterus’ that I’ve published on a blog and shared with friends,” she said, adding that she did not send the mocking letter to the bank.

“We really needed the new house,” Falcão said.

After closing on the loan, she filed a complaint with HUD.

Earlier this summer, HUD announced that the Irvine, Calif.- based mortgage lender Greenlight Financial Services will pay $20,000 to Stefanie and Jonathan Alvanos, who filed a complaint alleging discrimination. The lender also will pay $7,000 each to four other applicants.

The Alvanoses — she is a middle school teacher and he is a real estate and bankruptcy attorney — were about to have their first child and were seeking to refinance their home when Greenlight told them it couldn’t serve them because of the upcoming maternity leave.

“I couldn’t believe they would say ‘You are pregnant and can’t refiance,’ ” Jonathan Alvanos said in a phone interview from their home in Rancho Santa Margarita, Calif. “They called it just another form of disability. But I thought that’s discrimination on a few different levels. You basically are telling me that my wife and unborn child are a liability. I contacted HUD. I’m glad to know they can’t just walk over everyone.”