Four Democratic senators led by Bob Casey of Pennsylvania plan to send a letter to President Trump on Wednesday seeking an executive order to help preserve call center jobs by banning federal contractors from offshoring such posts. The senators said they also plan to push for legislation requiring that companies notify customers when a call is handled overseas and offer an option to transfer the call to a domestic call center.

“We are writing today to strongly encourage you to not only focus on bringing back manufacturing jobs, but service sector jobs as well; in particular customer service and call center jobs,” the senators wrote in the letter, a copy of which was provided to Fortune. “We urge you to take executive action and to support legislation to help protect and bring call center jobs back to the United States.”

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Three more Democratic senators agreed to sign the letter, making a total of seven, by the time it was sent to the president on Thursday. 

Preserving call center jobs has been an increasing focus of labor union activity. The issue was one of the core disputes in the bitter, seven-week strike by Verizon (VZ) workers last year that was settled only after the telecom giant promised to stop outsourcing unionized call center jobs. The issue was also raised this week by AT&T (T) workers negotiating a new contract.

Trump’s focus so far has largely been on manufacturing jobs, as he criticized moves such as Ford’s (F) plans to build a new plant in Mexico and Carrier’s plan to move some jobs to Mexico. But service sector jobs have also been leaving the country, the senators noted.

The senators’ letter also alleged a security risk from overseas call centers, which they said had inadequate security measures to protect customer data and could be a training ground for criminals who go on to crate scam call center operations.

The legislative proposal would be similar to a bill Casey introduced in 2013 that would have required disclosure of a call center location to consumers along with the option to transfer to a domestic call center. The prior bill also required the Department of Labor publicly to report companies that relocated call center operations overseas.

In addition to Casey, the letter was initially also signed by Senators Sherrod Brown (D-Ohio), Joe Manchin (D-West Va.), and Tammy Baldwin (D-Wisc.). Later signers were Senators Claire McCaskill (D-Missouri), Joe Donnelly (D-Ind.), and Heidi Heitkamp (D-N.D.). 

(This story was updated on January 27 to add three more senators who signed the letter.)