Labor regulators find merit in accusations by unions at Amazon and Starbucks.

In a sign that federal labor officials are closely scrutinizing management behavior during union campaigns, the National Labor Relations Board said Friday that it had found merit in accusations that Amazon and Starbucks had violated labor law.

At Amazon, the labor board found merit to charges that the company had required workers to attend anti-union meetings at a vast Staten Island warehouse where the Amazon Labor Union won a stunning election victory last month. The determination was communicated to the union Friday by an attorney for the labor board’s regional office in Brooklyn, according to Seth Goldstein, a lawyer representing the union.

Such meetings, often known as “captive audience” meetings, are legal under current labor board precedent. But last month, the board’s general counsel, Jennifer Abruzzo, issued a memo saying that the precedent was at odds with the underlying federal statute, and she indicated that she would seek to challenge it.

In the same filing of charges, the Amazon Labor Union accused the company of threatening to withhold benefits from employees if they voted to unionize, and of inaccurately indicating to employees that they could be fired if the warehouse were to unionize and they failed to pay union dues. The labor board also found merit to these accusations, according to an email from the attorney at the regional office, Matt Jackson.

Mr. Jackson said the agency would soon issue a complaint reflecting those accusations unless Amazon settled the case. The complaint would be litigated before an administrative law judge, whose decision could be appealed to the labor board in Washington.

Mr. Goldstein applauded Ms. Abruzzo and the regional office for taking “decisive steps ending required captive audience meetings” and said the right to unionize “will be protected by ending Amazon’s inherently coercive work practices.”

Kelly Nantel, an Amazon spokeswoman, said in a statement that “these allegations are false and we look forward to showing that through the process.”

At Starbucks, where the union has won initial votes at more than 50 stores since December, the labor board issued a complaint Friday over a series of charges the union filed, most of them in February, accusing the company of illegal behavior. Those accusations include firing employees in retaliation for supporting the union; threatening employees’ ability to receive new benefits if they choose to unionize; requiring workers to be available for a minimum number of hours to remain employed at a unionized store without bargaining over the change, as a way to force out at least one union supporter; and effectively promising benefits to workers if they decide not to unionize.

In addition to those allegations, the labor board found merit to accusations that the company intimidated workers by closing Buffalo-area stores and engaging in surveillance of workers while they were on the job. All of those actions would be illegal.

In a statement, Starbucks Workers United, the branch of the union representing workers there, said that the finding “confirms the extent and depravity of Starbucks’s conduct in Western New York for the better part of a year.” It added: “Starbucks will be held accountable for the union-busting minefield they forced workers to walk through in fighting for their right to organize.”

Starbucks said in a statement that the complaint doesn’t constitute a judgment by the labor board, adding, “We believe the allegations contained in the complaint are false, and we look forward to presenting our evidence when the allegations are adjudicated.”