One of the biggest selling points of Facebook’s ambitious plans for its new cryptocurrency, Libra, was that the social media company had 27 partners, including prominent outfits like Visa, Mastercard and Uber, helping out on the project.But some of those partners are approaching Libra warily. They signed nonbinding agreements to join the effort partly because they knew they weren’t obliged to use or promote the digital token and could easily back out if they didn’t like where it was going, said executives at seven of those companies, who spoke on the condition of anonymity because of the sensitivity of the negotiations.The doubts among Facebook’s partners add to a growing list of challenges for Libra, a new digital token that Facebook executives hope will one day become the foundation for a new kind of online financial industry.Interested in All Things Tech?The Bits newsletter will keep you updated on the latest from Silicon Valley and the technology industry.Companies are hesitant to associate themselves too closely with the Libra project because of Facebook’s issues with regulators around the world, the company’s shaky track record on privacy and how it treats corporate partners, and the uncertain legality of cryptocurrencies.Maxine Waters, the chairwoman of the House Financial Services Committee, has scheduled a hearing on the Libra cryptocurrency.CreditErin Schaff/The New York TimesImageMaxine Waters, the chairwoman of the House Financial Services Committee, has scheduled a hearing on the Libra cryptocurrency.Maxine Waters, the chairwoman of the House Financial Services Committee, has scheduled a hearing on the Libra cryptocurrency.CreditErin Schaff/The New York TimesThough it was announced just a week ago, the Libra effort has already drawn scrutiny in Washington. Maxine Waters, the chairwoman of the House Financial Services Committee and a Democrat from California, quickly scheduled hearings to examine Libra and told Facebook to stop development of the project until big questions are answered.The House hearing is set for July 17. The Senate is expected to hold a hearing on the same issue the day before.Jerome H. Powell, chairman of the Federal Reserve, said on Tuesday that the central bank would be looking at Libra “very carefully” given its potential scale. “I think that our expectations from a consumer protection standpoint, from a regulatory standpoint, are going to be very, very high,” Mr. Powell said at an event at the Council on Foreign Relations in New York.European regulators have also asked for more details about the project.Facebook said the 27 partners that it announced last week were giving at least $10 million and joining an association that would govern the Libra cryptocurrency, which is set to be introduced next year.Editors’ PicksWhen You’re Told You’re Too Fat to Get PregnantGiant Squid Reappears on Video, This Time in U.S. WatersWhen ISIS Killed Cyclists on Their Journey Around the WorldBut no money has changed hands so far. A number of partners said they would decide whether to join the association and make the payment after there is more clarity on how Libra will work, the executives from the seven companies said.A Facebook spokeswoman, Elka Looks, said in a statement that the company plans “to engage in healthy dialogue and debate with our fellow founding members, and to welcoming additional members over the coming months.”“We know this will take time and it won’t be easy, but together we will be able to make the Libra mission a reality,” Ms. Looks said.A spokesman for the Libra Association, Dante Disparte, said that since the announcement last week, the association has heard from a flood of companies interested in being members. He said the association, which will manage Libra, will most likely have a waiting list for those wanting to be among the 100 initial members it hopes to start with next year.Facebook had hoped its partners could help Libra handle some of the critics and give the project some distance from the social networking giant and its recent legal problems. But even before the project began, potential partners had their own concerns.Facebook approached a number of big financial companies, including Goldman Sachs, JPMorgan Chase and Fidelity, about participating in the project, according to two people briefed on the discussions. The financial companies declined to join, in part because of regulatory questions about cryptocurrencies, the people said.Press officers for the banks all declined to comment. A spokeswoman for Fidelity said the company was continuing to monitor the project.