As part of its agreement with the coalition of investors, which also includes other pension funds for unionized workers, Apple agreed to hire a third-party firm to conduct the assessment, the coalition said in a letter to the company’s chairman on Tuesday. The letter also laid out recommendations for the assessment, which include hiring a firm that has expertise in labor rights and that is “as independent as practicable.”

Apple’s federal filing did not refer explicitly to a third party, and the company declined to comment further.

Members of the investor coalition controlled about $7 billion worth of Apple stock as of last week, out of a market capitalization of more than $2 trillion. In its financial filing announcing the assessment, Apple offered few details, saying that it would conduct the assessment by the end of the year and that it would publish a report related to the assessment.

Last year, workers voted to unionize at two Apple stores — in Towson, Md., and Oklahoma City — and workers at two other stores filed petitions to hold union election before withdrawing them.

Many workers involved in union organizing at the company said they enjoyed their jobs and praised their employer, citing benefits like health care and stock grants and the satisfaction of working with Apple products. But they said they hoped that unionizing would help them win better pay, more input into scheduling and more transparency when it comes to obtaining job assignments and promotions.