MiMedx, a fast-growing tissue-graft developer, has financial ties to more than 20 doctors, according to a review of doctors’ disclosures by The Wall Street Journal, but the company hasn’t reported these payments to the government under a 2013 law.

The company says its products, made from donated placental tissue, aren’t among those that require a disclosure of doctor payments. At least one of MiMedx’s direct competitors,Osiris Therapeutics Inc., regularly provides information on its ties to doctors and reported $1.03 million in such payments in 2016.

MiMedx announced Tuesday that its board had engaged independent advisers to review its sales practices. News of the review, and that MiMedx was delaying the release of its 2017 financial results, caused the company’s shares to fall 40% in one trading day.

Shortsellers have accused MiMedx of engaging in improper sales tactics to meet quarterly earnings forecasts, allegations the company has repeatedly denied. MiMedx, whose products are used in wound care and surgical procedures, was named the fifth-fastest growing public company in the country by Fortune magazine late last year.

Based in Marietta, Ga., MiMedx makes skin grafts and injectable products from human placental tissues donated by new mothers, post-delivery. The company previously had said it expected to report 2017 sales of $325 million, up from $245 million in the prior year.

Before the disclosure of the sales-practice review, MiMedx shares had been up more than 70% over the past 52 weeks. Now they are roughly flat for the period, giving the company a market capitalization of around $1 billion.

Since 2013, most biotechs, drug and medical-device makers have been required to disclose payments or gifts they make annually to doctors and teaching hospitals, under the Physician Payments Sunshine Act. The law purports to educate patients about financial ties between doctors and drug companies and to “stop dishonest influence on research, education, and clinical decision-making,” according to the Centers for Medicare and Medicaid Services, the government agency that oversees the program.

Every June, CMS publishes data detailing the prior year’s payments to doctors for consulting fees, as well as for entertainment, research, speaking fees and travel costs. The most recent data, from 2016, shows that manufacturers made $8.19 billion in such payments.

The CMS website shows no record of stock grants, speakers’ fees and research support provided by MiMedx to doctors and their hospitals in recent years, though its financial relationships with at least 20 doctors appear in public disclosures that were reviewed by the Journal.

Executives at MiMedx contend the company doesn’t have to report its payments to physicians because its products are classified as tissues under Section 361 of the Public Health Service Act and it is therefore not a “applicable manufacturer.”

MiMedx’s website states that it has “received an opinion from CMS which confirms that MiMedx does not have a need to report at this time.”

But Tony Salters, a CMS spokesman, said the agency doesn’t provide such opinions. Outside of a compliance action, he said in an email, the agency doesn’t give individual determinations, in writing or otherwise; rather, it provides general guidance that companies can consider.

Asked how MiMedx could have received an opinion from an agency that says it doesn’t provide them, Parker H. “Pete” Petit, MiMedx’s chief executive, referred questions to Andy Ruskin, at Morgan, Lewis & Bockius in Washington, D.C., MiMedx’s regulatory lawyer.

Mr. Ruskin declined to discuss specifics about MiMedx’s discussions with CMS. In general, he said, “how you act on the feedback you are getting from the government is going to be the same irrespective of whether the government labels what they issue an opinion or labels it as guidance or does not provide any label whatsoever.”

A company that knowingly fails to report doctor or hospital payments can face a maximum penalty of $1 million a year.

Asked about MiMedx’s payments, Mr. Petit said, “We have very few agreements with doctors.”

However, details of financial relationships between MiMedx and at least 20 doctors appear in public disclosures required by medical associations, including the North American Spine Society and the American Urological Association, when doctors appear on panels, publish papers or make presentations at conferences.

Doctors’ disclosures to the spine society show MiMedx paid the Hospital for Special Surgery in New York City as much as $500,000 in 2017 for research conducted by Alexander P. Hughes, a spinal surgeon, and Andrew A. Sama, an associate attending orthopedic surgeon. In 2015 and 2016, MiMedx made payments of as much as $70,000 to the hospital. The payments, disclosed in ranges rather than precise amounts, support research using a MiMedx product in spinal surgery to see if it decreases the need for subsequent operations.

A hospital spokeswoman said the project is ongoing and declined to comment on the payments. She declined to make the doctors available.

Lee C. Rogers, managing partner of Amputation Prevention Experts Health Network, began receiving hourly consulting payments from MiMedx around 2013, he said in an interview, adding that he stopped working for MiMedx in 2015 because his practice changed.

In 2014, Dr. Rogers ran unsuccessfully for Congress in California. Federal Election Commission records show Mr. Petit, MiMedx’s founder, and his wife, Janet, contributed $5,200 to the Rogers campaign. Both Dr. Rogers and Mr. Petit confirmed the donation.

When the Physician Payments Sunshine Act went into effect in 2013, Dr. Rogers criticized its disclosure requirements in a post on a podiatry website. The law, he said, would have a “tragic” impact on industry conferences because it could reduce “sponsorships from drug and device companies.” He declined to provide his current views.

Others praise the Sunshine law, however. Adriane Fugh-Berman, a professor of pharmacology and physiology at Georgetown University Medical Center, said: “Being able to see how much money your doctor is getting from whom for promoting what drugs may make a difference in your choice of physicians or your trust in physician recommendations.”