Dear Mr. Freyberg,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located the series titled General Index to Litigation Case Files, 1904 - 1951 in the General Records of the Department of Justice (Record Group 60) that included a card for Harold Laski dated 29 March 1949. It indicated that there is a case file for Harold Laski [case number 149-06-2-4] questioning if Laski was obligated to register under the Foreign Agents Registration Act while on a lecture tour in the U.S. For access to and/or copies of this case file, please contact the National Archives at College Park - Textual Reference (RDT2) via email at firstname.lastname@example.org.
We hope this is helpful. Best of luck with your research!