Report says the Christian Democrats party conference is also expected to return Merkel for the ninth time as party chief.
Meanwhile, the party is also expected to toughen its stance on refugees.
Report says the CDU party conference is also expected to return Merkel for the ninth time as CDU chief.
She secured 96.7 per cent of the vote when the ballot for party leader was last held two years ago.
A poll published in November showed 64 per cent of those surveyed supported the chancellor making a bid for another term as head of Europe’s biggest economy in the September 2017 election.
However, the size of Tuesday’s vote for Merkel would underscore the degree to which her political standing has suffered as a result of the refugee crisis, which has triggered deep divisions in her party’s ranks.
The chancellor signaled on Monday that the CDU planned to toughen its stance on refugees, including measures to step up deportation of failed asylum seekers.
The party’s moves to set a more hardline approach to refugees at its conference came in the wake of a string of state election successes by the right-wing populist Alternative for Germany (AfD).
In particular, the AfD has siphoned votes from the CDU after capitalising on anger in parts of the German electorate over Merkel’s liberal refugee policy.