(Reuters) - The leader of one of the largest U.S. labor unions on Thursday called on top asset managers to review Tesla's valuation as the electric carmaker's shares have slumped 30% so far this year.

Randi Weingarten, president of the American Federation of Teachers, wrote to top fund firms with Tesla shares including BlackRock ( BLK ), Vanguard and T. Rowe Price ( TROW ), saying she was concerned about the potential impact on members' pension portfolios.

On Tuesday, Tesla's market capitalization slid below $1 trillion for the first time since November after data showed sales fell in Europe in January.

In an interview, Weingarten said the union was not looking for the funds to sell the stock but was concerned asset managers may be overlooking Tesla's problems because of the influential role Tesla CEO Elon Musk has taken as a top adviser to U.S. President Donald Trump.

"Our concern is that because of the politics, and the proximity Mr. Musk has to Mr. Trump, they are standing down on this rather than doing their jobs," said Weingarten. She has criticized various Trump actions like his goal of closing the Department of Education.

Vanguard and T. Rowe Price ( TROW ) representatives declined to comment. BlackRock ( BLK ) and Tesla did not immediately respond to requests for comment.

Weingarten's letter on Tesla cited issues including its fourth quarter profit decrease and competition for EV chargers.