The number of green cards to be issued to skilled migrant workers will be based on research by Forfás on skills shortages in the economy.
This is one of a number of provisions in the Employment Permits Bill due to be published by the Minister for Enterprise, Trade and Employment, Micheál Martin, on Wednesday.
Government sources have suggested that the number of green cards issued in the initial years of the scheme will be in the low thousands.
They are likely to be issued to workers in sectors such as science and technology, engineering, the health service and the IT sector, where skills are in short supply.
The green cards, which will be issued for a minimum of five years, are being introduced in response to growing competition for highly skilled migrant workers in Europe and the US.
Card holders, as with all other people legally resident in the State, will be able to apply for citizenship after five years of residency.
Assessments of skills shortages by Forfás and the Expert Group for Future Skills Needs, a body appointed by the Government to advise it on labour shortages, will influence how many green cards are issued.
Both of these groups are engaged in research and consultation on the types of skills for which green cards should be granted.
This work will form the basis of a policy paper to be published by Mr Martin later this year. The numbers will ultimately be at his discretion.
The legislation will affect nationals from outside the European Economic Area, which comprises the EU's 25 member states as well as Norway, Iceland, Liechtenstein and Switzerland.
The existing work permit regime for skilled workers has been criticised as bureaucratic and inflexible by lobby groups in the private sector.
At present, skilled migrant workers in certain sectors may work here and bring their family members under a work visa or authorisation scheme, which is renewable every two years.
Others must obtain a work permit, renewable every 12 months.
It is expected that, unlike standard work permits, green cards will be issued to individual workers who will be free to change employment within their area of expertise.
More than 1,300 working visas and work authorisations were issued in 2004.
The Minister is also due to announce a series of changes to the work permit system aimed at protecting lesser-skilled workers from exploitation.
However, unions and migrant worker support groups are likely to say the changes will not go far enough.
Standard work permits will still be held by employers, although workers will be able to have copies of their permits.
Employers will also be prohibited from holding on to documents such as workers' passports.
The legislation is expected to include fines of up to €50,000 or five years in prison for employers found guilty of serious breaches of labour law.