The biggest rail workers union demanded information today about a media "undercover surveillance operation" against the union and its general secretary.
The Rail Maritime and Transport (RMT) union claimed that "operatives" from News International (NI) trawled bins at the union's national conference last year, and national officials, their families and neighbours were "harassed".
The RMT has written to NI's lawyers demanding to know which journalists were involved in an alleged surveillance operation against its leader Bob Crow.
In evidence to the Leveson inquiry, the RMT has alleged there was a "long and sustained" campaign against the union by newspapers, including News International titles, dating back to 2002.
An RMT spokesman said: "RMT lawyers have written to News International's lawyers today demanding information on the surveillance operation mounted against the union and asking for the names of those involved.
"RMT has also submitted a full dossier of information to the Leveson inquiry dating back nearly a decade and we expect to be called to give further evidence in the near future."