Welsh Conservatives leader Andrew RT Davies has warned turnout for the 5 May vote could be the lowest so far.
On Sunday, Labour's Ken Skates told BBC Radio Wales he was "personally in favour" of compulsory voting.
His party - which has previously rejected the idea - declined to comment.
The Welsh Conservatives, UKIP, Plaid Cymru and Welsh Liberal Democrats said they were all against the introduction of compulsory voting.
Mr Skates, who is standing for re-election as an AM in Clwyd South, told the Sunday Supplement programme he was "disappointed" by the turnout in the constituency during the last assembly election - about 40%.
"It's always of concern when turnout reduces. I'm personally in favour of compulsory voting and always have been," he said.
"I think it's important to examine all possibilities to improve turnout using digital technology, but also considering compulsory voting."
Eleven countries enforce participation in elections - including Australia, which issues fines -  and a dozen more have some kind of mandatory voting legislation that is not enforced.
Mr Skates said the UK's European Union membership referendum had also "caused confusion", with the 23 June vote being so close to the assembly election.
The lowest assembly election turnout was 38.2% in 2003.
However, Mr Davies said compulsory voting would allow politicians to "abdicate their own responsibility for increasing public engagement with politics".
He added: "We need to make politics more engaging, interesting and representative - not hold a gun to people's heads and force them to vote."
A Welsh Lib Dems spokesman said the party "believes people should be able to keep their right not to vote".
UKIP also poured cold water on the suggestion, with MP Douglas Carswell saying: "Government should not penalise voter disengagement.
"Instead we should have politicians who engage the public and policies worth voting for".
Compulsory voting should be considered to boost turnout at Welsh Assembly elections, Labour's deputy minister for culture, tourism and sport has said.