It could only supply individual ministers (e.g. in finance, education or foreign affairs) to successive governments after 1923 in cooperation with the National Democrats and the peasants' party (Chjeno-Piast).

In the 1922 presidential elections, the Popular National Union nominated Count Maurycy Zamoyski to counter the centrist Gabriel Narutowicz and the socialist Stanisław Wojciechowski of the Polish People's Party “Piast”.

After the May 1926 Coup, the Popular National Union gradually lost its influence and power in the wake of internal schisms and conflicts under the rule of its rivals, the Sanation regime.

At the beginning, the ZLN was a federation of political parties, but the summer of 1919 saw the departure of the Christian-National Workers Club (Chrześcijańsko-Narodowy Klub Robotniczy) from its ranks.

On 16 January 1919, a non-aligned government arose with the cooperation of ZLN members Władysław Seyda as Minister of the “Prussian” District, Józef Englich in finance, and Reverend Antoni Stychel as Deputy Speaker of Parliament.

Later that same year, a nominee of the National Democrats, Maurycy Zamoyski, was defeated by Gabriel Narutowicz in a runoff fifth round of voting in parliament.

On 17 May 1923, the Lanckorona Pact saw representatives of the ZLN, the Christian-National Labour Party (Chrześcijańsko-Narodowe Stronnictwo Pracy), and PSL “Piast” (that is, some right-wing and centrist parties) agreeing to a broad set of philosophical and operational principals, including Polish social policy towards the Eastern (and therefore minority-heavy) borderlands, the assignment of governmental portfolios exclusively to Poles, and joint policies against the political left.

From the ZLN's point of view non-Poles in the Republic were considered second-class citizens up to the moment they underwent linguistic and cultural assimilation.

A "Supreme Council" (Rada Naczelna) with Stanisław Głąbiński as president and a Board of Directors (Zarząd Główny) numbering 30 emerged from the reorganization.

From November 1923, Prime Minister Grabski tried to come to a political understanding with representatives of national minorities in Poland; this created conflicts within the government.