Jim Sillars said the Continuity Bill was part of a “tactical package” presented by the Scottish Government to hijack the EU withdrawal process.
He was speaking ahead of a legal challenge to the legislation’s competence being heard in the UK Supreme Court this week.
On Tuesday the UK government will begin its legal challenge to the Holyrood legislation, which has been proposed as an alternative to the UK government’s EU Withdrawal Bill.
Scottish Government ministers have put forward the Continuity Bill because they believe the UK government withdrawal legislation amounts to a power grab from Holyrood.
The Scottish Government objects to UK government plans to temporarily freeze the transfer of powers in 24 areas. But Sillars, who supports Brexit, disagrees that the EU Withdrawal Bill is a power grab.
Yesterday Sillars said: “The Continuity Bill is part and parcel of the tactical package that the SNP government has in fact produced to try and prevent exit from the European Union.
“So far everything has failed and we have to wait and see whether this one fails or not.”
Two days of evidence will be heard this week and a judgment is expected in October.
A SNP spokesman said: “This bill is about protecting devolution from the Tory power grab. The Tories now think they can do anything they want to Scotland and get away with it so it is more important than ever to protect the Scottish Parliament.”