Alex Salmond has appealed to the “independence family” to back his new party, as he made a final pitch for votes for Alba.
In an eve-of-poll message, the former first minister said voting SNP in the regional list ballot would let pro-Union MSPs “in by the back door”.
Alba is only running candidates in the regional lists, urging supporters to vote SNP in the constituency ballot.
Mr Salmond hopes to return to Holyrood as leader of the new party, which launched its election campaign on March 26.
In an online video for supporters, he said: “I want to address some remarks in particular to the independence family – that 50% or more of Scots who are already convinced of the case for independence and are looking for when it’s going to happen and how it’s going to happen.”
Claiming the SNP will not pick up seats on the regional lists due to a strong showing in the constituency vote, he said: “An SNP vote is sometimes described as a wasted vote on the second ballot paper.
“It’s actually worse than that. An SNP vote in the second ballot paper actually lets the unionists, Labour and Tory MSPs, in by the back door.”
He said the Scottish Greens are a “fine and estimable party” but are “soft” on independence.
Polling has been inconsistent for Alba throughout the campaign, with analysis of some opinion polls projecting it will not win any seats. However a Panelbase poll last week predicted it could pick up as many as eight.
The most recent polls put the Greens ahead of Mr Salmond’s party in the regional list vote.
Mr Salmond said Alba is “the new kid on the block, the plucky underdog of Scottish politics, the people who are trying to gain a bridgehead in the Scots Parliament to develop some urgency into the independence case”.