The three justices of the Legislative Council emphasize that anyone convicted in Sweden should serve their sentence in Sweden.
"Various well-founded exceptions to this rule can be considered, but a lack of prison places is not such a reason," they write.
The government has justified the proposal by saying that there are too few places in Sweden. In June last year, an agreement was signed with Estonia - that is, even before there was legal support for it - to rent 600 places.
Despite the criticism, the Legislative Council sees no "absolute obstacle" to the proposal, but wants to limit the law's duration. The government has not set any time limit.
