Representatives of all three parties met Thrsday and agreed on cooperation ahead of the local elections in Riga, Unity's chairman Andris Piebalgs said.
Raivis Dzintars, the co-chairman of the National Alliance, said the coalition partners would hold regular meetings to agree on a cooperation framework before the elections.
It has also been agreed that after the local elections - if they get enough votes - the three parties would form a new ruling coalition in the Riga City Council and the party which would have received the largest number of votes would get the coveted mayor's office.
The position of Riga mayor is one of the most powerful in the country and Ušakovs, of the opposition Harmony party, will be difficult to unseat. Ušakovs himself had previously questioned the ability of the coalition parties to offer a joint candidate, and his prediction appears to have been borne out already.
He is serving a second successive two-year term and polls suggest he still has strong support, despite his image taking a knock recently in connection with chaotic roadworks in the capital.
But other initiatives such as the opening of new public parks and the renovation of school facades have proven popular with Riga residents.
Piebalgs said the politicians today had agreed on cooperation in principle but there was no need to sign a formal agreement, at least not for now.
Unity had proposed to the Greens and Farmers Union and the National Alliance to create a joint ticket in the 2017 local elections in Riga with the aim to end the rule of the current coalition of Harmony and oys sister party Honor to Serve Riga.
The National Alliance was reportedly willing to team up but the Union of Greens and Farmers was against the idea.
When asked whether the Unity was considering the possibility of a joint ticket with some other political force, Piebalgs said he would report to the party's board the results of the today's meeting and then he might request a mandate to talk to other parties which were interested in cooperation.
Currently Unity has eight seats in the 60-member Riga City Council and sits in the opposition together with the 12 councilors representing the National Alliance. ZZS has no representatives in the current Riga City Council.