He asked that the department's Committee on Foreign Investment in the United States review the sale, and block it if it presents undue risk.
The congressman said because of concerns raised by that committee last year, a sale was called off of the Hotel del Coronado near San Diego to Chinese insurance giant Anbang. Lowenthal speculated "that the hotel's proximity to the U.S. naval base factored prominently."
Meanwhile, the UNITE HERE labor union, which seeks to represent Westin's workers, circulated Lowenthal's letter and added in a news release this week that the sale "raises national security questions because the hotel is next door to the U.S. Customs and Border Protection" offices in Long Beach.
The Utah Retirement Systems which provides retirement and insurance benefits for state, local government and school employees in Utah acknowledges an ownership interest in the Westin Long Beach Hotel, but declines to say whether a sale is in the works.
"We periodically review unsolicited offers to buy the hotel," said URS spokesman Brian Holland.
"However, it is not being publicly marketed at this time nor is it under contract," he added. "Like other institutional investors, we do not publicly discuss specific proposed transactions. But we always follow all applicable laws regarding our financial transactions."
He said URS is the majority shareholder of a limited liability corporation that owns the hotel, but a separate entity manages it and is the employer of the hotel's workers.
While some may be surprised that the pension fund owns a hotel, Holland said, "as typical of large pension funds, URS invests in diverse assets, including real estate, as part of our balanced strategy designed to generate our assumed investment rate of return over the long run."
The URS on its website said it manages assets worth nearly $27 billion.
Lowenthal noted in his letter that the hotel is at the second-busiest port in America and next door to customs offices there that house sensitive information.
Also, "U.S. government clients with sensitive national security information" have contracts with the hotel and use it often, he said, including the Defense Department, Homeland Security, Justice Department and the Drug Enforcement Administration.
He noted that President Barack Obama quit using the Waldorf Astoria Hotel in New York City after it was bought by the Chinese firm Anbang, which he said The Associated Press attributed to "fears of espionage."
Before the hotel is sold, Lowenthal asked that Treasury find whether "any potential buyers of the Westin Long Beach have ties to the Chinese government or other foreign state actors."
He also wants to know "what safeguards are or will be put in place to protect the exposure of sensitive national security and commercial data processed by U.S. Customs and Border Protection" next door.
And he wants to know what assurances, if any, hotel customers may have "that sensitive information will be protected from unwanted surveillance in the hotel under new ownership."
The UNITE HERE union in its news release supported the requests by Lowenthal. Jordan Fein, a senior research analyst for the union, said the hotel's workers do not have union representation now. He said some seek unionization, and UNITE HERE seeks to allow votes on that without improper interference from owners.