S. Rept. 116-188: TSA Credential and Endorsement Harmonization Act of 2019, Report, Including Cost Estimate of the Congressional Budget Office, December 19, 2019 [open pdf - 407KB]
From the Purpose of the Bill: "This legislation requires the Transportation Security Administration (TSA) to develop a plan to expand TSA PreCheck eligibility to relevant Transportation Worker Identification Credential (TWIC) or Hazardous Materials Endorsement (HME)-endorsed individuals. The bill would allow TSA to establish an alternative fee structure to carry out the program."
S. Rept. 116-188; Senate Report 116-188
U.S. Government Publishing Office: http://www.gpo.gov/