A union-aligned investment group has written to Amazon, Walmart and Alphabet seeking details on how U.S. President Donald Trump’s immigration policies are affecting the companies’ finances, labour supply and supply chains, according to documents seen by Reuters.

SOC Investment Group, which owns less than 1percent of each of the three companies, asked the firms to explain how they plan to navigate a proposed $100,000 fee for new approvals of H-1B visas, widely used to hire skilled foreign professionals. Amazon, Walmart and Google-parent Alphabet are among the largest recipients of H-1B visa approvals in the United States.

The group has a track record of using shareholder engagement to push companies on social and governance issues, including persuading some firms to conduct racial equity audits and disclose more information about their lobbying activities.

“The availability of skilled labour is really critical to the long-term performance of a company,” SOC Investment Group Executive Director Tejal Patel told Reuters. “If companies cannot keep up with consumer demand or competition because they are unable to hire the right people, that poses a risk to shareholder value over the long term.”

In its letters, SOC also asked Amazon and Walmart to detail how Trump’s immigration policies are affecting the trucking and farming sectors that support supermarket supply chains. The policies have included immigration raids on farms, which the group said could disrupt the flow of goods needed to keep store shelves stocked.

SOC Investment Group and affiliated funds hold roughly 17 million shares of Walmart, 31 million shares of Amazon and 41 million shares of Alphabet, according to the firm.