It shall be unlawful for any two or more such telegraph or telephone companies, telegraph press associations, railroad companies or leased wire firms or private individuals doing business in this state and employing telegraphers, to conspire, contract, mutually agree or co-operate to discriminate against, blacklist or refuse employment to any telegrapher merely on account of such telegrapher's affiliation with or membership in any lawful organization or trade or labor union of telegraphers.