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As if there aren't enough forms of financial stress for American workers these days, you can add another: Employees are worried over their potential to default on 401(k) loans.

They're happy they have the option to take the loans—don't get them wrong—but they're also worried about how they'll manage to pay them back, according to a new study from fintech firm Custodia Financial and market research firm Greenwald & Associates.

The study, titled "Missing Voices: What 401(k) Borrowers Can Add to the Loan Program Conversation," found that 91 percent of employees find it valuable to have the loan option, 70 percent say that if they lost their jobs they'd have a tough time paying the money back. And the younger they are, the more worried they are; millennials aged 25–34, topped the list, with 69 percent worried about it. Fifty-four percent of those aged 35–44 came next, followed by 49 percent for ages 45–54; 28 percent for ages 55–64; and 44 percent for ages 65-plus.