The Commission, the executive body of the European Union, is expected to request the divestment of Telia's Finnish mobile unit and its cable TV business Comhem.
If the companies refuse to meet the conditions set by EU competition authorities the Commission will open a three-month detailed investigation of the deal.
But one Commission official requesting anonymity said that Telia, Sonera and the Commission are in agreement about the required divestments. "There is a pretty good chance the deal will be waved through tomorrow," the official said.
Telia offered 1.5 of its own shares for each Sonera share in late March in a bid worth €7.4bn (£4.7bn) at the time. The offer valued Sonera at a 16% premium to the market price.
However, sharp falls in the value of telecom stocks in recent weeks slashed the value to €4.8bn (£3.1bn) on Tuesday afternoon, with the premium paid for Sonera shrinking to about 6%.