The five federations call on citizens who are planning to sign the petition to do as soon as possible.
The unions' signature-collecting drive was launched on June 9 and lasts until June 23.
By 23 June, they should collect slightly over 450,000 signatures, that is 10 percent of the entire electorate, in order to be able to launch the referendum's procedure.
The trade union federations lambasted the government-sponsored draft amendments to the Labour act (ZOR) which they deem to be harmful for collective bargaining and agreements.