Safety concerns have been raised over the use of foreign workers from lightly regulated regimes by North Sea operators.
A Holyrood committee has said the UK Coastguard Agency must respond to fears the safety of UK seafarers is at risk as a result of so-called "flag of convenience" practices.
The RMT union has described conditions on some vessels operating in UK waters as "purgatory".
A report by The Scottish Parliament's Economy, Energy and Tourism Committee has also called on the Scottish Government to do more to assess the impact of the oil crisis on Scotland's economy.
Unions told the committee of an increasing exclusion of UK seafarers from the North Sea due to "employers using gaps in employment legislation to employ non-UK seafarers below the UK minimum wage".
The STUC said these practices were not evident in other North Sea jurisdictions, and that "there is no doubt" the health and safety of UK seafarers was being compromised.
Jake Molloy, regional organiser of the RMT union, said: "I have done International Transport Workers Federation (ITWF) inspections on some vessels that have been flying the flag of convenience, and I know that the Filipino and Indonesian workers look upon us as the police arriving to save them from purgatory.
"The conditions on some of those ships are appalling (with) less competent, less able and less willing workers being exploited in order to exploit our natural resources."
The ITWF defines a flag of convenience ship as one that flies the flag of a country other than the country of ownership.
It said this can mean "very low wages, poor on-board conditions, inadequate food and clean drinking water and long periods of work without proper rest" so operators can benefit from "minimal regulation, cheap registration fees, low or no taxes and freedom to employ cheap labour from the global labour market".
Mr Molloy told the Committee British seafarers had taken a 25% wage cut resulting in a salary of only £23,000 a year and now work six weeks on, six weeks off "to try to save their jobs and compete".
He called for action to restrict employment in EU waters to EU and UK seafarers who are paid at minimum wage.
The Committee said: "We invite the Maritime and Coastguard Agency to respond to the concerns raised with the Committee by trade union representatives in respect of health and safety on flag of convenience vessels and the remuneration of non-UK seafarers below the UK minimum wage.
"We ask also for an update on recent UK Government engagement at an EU level to protect and enhance the working conditions of UK seafarers."
The Committee also recognised the challenge of assessing the impact the oil crisis has had on the Scottish economy.
But it called for more work to be done amid evidence suggesting the number of jobs lost or at risk "is likely to be much higher" than the 6,000 "direct" jobs estimated by the Scottish Government in September.
The actual figures did not include self-employed subcontractors, the Committee said.