Communications Workers' Union leader Mr Con Scanlon has told members they must move from the protected industry of old, where they could dictate the pace of change, and adapt to today's highly competitive market, where change is frenetic.
They could only survive by recruiting members in new private companies.
He told delegates at yesterday's session of its biennial conference in Limerick they had to expand from An Post and Eircom into the wider telecommunications industry.
He said the CWU now represented workers in over 20 companies and would be electing members to its national executive, for the first time, from these new members.
The new members are likely, however, to emerge from Vodafone, where the CWU has a strong presence after staff transferred from Eircom when its mobile phone subsidiary Eircell was sold off.
Mr Scanlon stressed that the CWU had to intensify its recruiting and organising activities.
"The future success and viability of this union depends on recruitment of new members. They are the lifeblood of the organisation and we simply cannot afford to be lax or remiss in our approach to maximising membership in existing companies or in seeking to organise in new companies."
Mr Scanlon said that the CWU's priority was "to organise all workers in the communications industry, many of whom are on low pay, or have little security or protection in an industry that has been going through turmoil in recent years".
However, he added that this was "easier said than done".
"We know from experience that employers are only too ready to put pressure on employees to prevent them joining our union."
He also called for changes in the new procedures under the Industrial Relations (Amendment) Act on union recognition.
He said the long drawn-out process lasting up to two years was "all too easy for employers to abuse" and "frustrate the desire of workers to be represented by their union.
"The time has come for the trade union movement to step up the pressure on the Government and employers that we will not tolerate this type of behaviour any longer."
"We should move this issue to the top of the trade union agenda," he said.