Migration Watch UK said Commonwealth immigrants who have not qualified for British citizenship could "significantly influence" the next General Election if voting is close.
Chairman Sir Andrew Green said:
One example is that a student visitor from a Commonwealth country planning to study for six months would be allowed to enrol on the electoral register and vote in a parliamentary election if one was held during the duration of his or her stay.
This is clearly absurd. The issue is one of basic fairness.
If people want to participate in deciding the future of our country they should at least become citizens.
More top news
Jersey has been named in a list of the top 10 best European islands for travellers.
The findings of the Chilcot inquiry into the Iraq War may not be published this year, according to reports.
Taking more than the recommended daily amount of over-the-counter vitamins may increase the risk of cancer and heart disease by up to 20%.