WASHINGTON -- It was once part of President Barack Obama's "We Can't Wait" economic agenda. But now the wait might be getting even longer.

The Labor Department is considering delaying a long-awaited rule that would extend new workplace protections to home care workers -- a possibility that has advocates for low-wage workers steamed.

In a letter addressed to Labor Secretary Tom Perez on Monday, more than 40 labor and advocacy groups said that they were "alarmed" by suggestions that officials might delay the new regulations and put a "historic workplace victory in jeopardy."

"The basic rights of two million home care workers -- predominantly women and disproportionately women of color -- once again hang in the balance, as the administration appears at risk of faltering in the face of opposition," they wrote.

The letter included signatures from the AFL-CIO labor federation, American Psychological Association and the National Employment Law Project, among others.

The new rule would guarantee minimum wage and overtime protections to home care workers, a class that's been carved out of such basic provisions for decades. Home care workers tend to the elderly and people with disabilities in their homes, and many of them work long hours and are paid relatively low wages for their efforts.

For years, labor groups had demanded that Congress or the executive branch rectify what they deemed an injustice, and last September it appeared they had finally gotten their wish. The White House announced that as of 2015, home care workers would be covered under the Fair Labor Standards Act, the Great Depression-era law that established minimum wage and time-and-a-half overtime pay for hourly workers.

But MSNBC first reported on Friday that the Labor Department was thinking about holding off on the rule's implementation due to concerns from unnamed stakeholders.

"We're flabberghasted," said Deane Beebe, spokeswoman for PHI, an advocacy group for home care workers. "Home care workers have been waiting for years for basic labor protections that most working Americans already have. They can't snatch it away at the last moment."

PHI attributes wage stagnation and high turnover rates in the industry to the fact that workers lack basic labor protections. The group has agitated for years for the reform.

Home care providers and industry groups have long opposed extending the wage standards to home care workers, arguing that it would raise costs on businesses and ultimately consumers. That opposition has not abated since the White House announced last year that the new rule would go into effect.

The National Association for Home Care & Hospice, an industry lobby, told its members last week that it had enlisted Sen. Mike Johanns (R) of Nebraska to try to pressure the Labor Department to sit on the rule. Nebraska is home to Home Instead Senior Care, a major home care provider that's been among the rule's more outspoken critics.

"A major effort to get signers on to the Senator Johanns letter might help to sway the Department of Labor," the lobby wrote. "The support to date has come only from Republican senators. It is expected that this will continue."

At this point, the Labor Department may be more concerned with the objections raised by state Medicaid programs, which ultimately pay the salaries of many home care workers. The National Association of Medicaid Directors has asked that officials wait another year and a half to roll out the rule. As MSNBC reported, the group claimed that it doesn't have the tools in place yet to comply with the requirements.

In their letter Monday, the labor groups noted that New York and California are already moving ahead under the reforms, and that other states had begun tracking workers' hours to account for the new overtime requirements.

"Some have even openly admitted to ignoring the rule over the past year," they wrote. "A delay would reward this intransigence. And it would exacerbate regional discrepancies in worker pay, ensuring that poor working women of color remain poor in the states where they need the wage increase the most."

The Labor Department declined to comment on any possible delays.