The two pre-election adversaries began negotiating a coalition deal last week, more than two months after an inconclusive March 4 election produced a hung parliament.
A new Italian government was put on hold on Monday after the leader of anti-establishment Five Star Movement asked President Sergio Mattarella for a few more days to form a coalition with the far-right League.
His words were backed up by Guglielmo Picchi, an MP and senior policy adviser for Lega.
"We're in the final stretch", Salvini said in a Facebook video.
"It is like they are part of the Franco-German axis".
The Five Star Movement and League parties were continuing to work on a government deal on Wednesday afternoon, with the leader of the M5S saying he and his League counterpart were prepared not to be part of the government if needed.
"A minister from the League who would work on security and border control would be a guarantor that whoever comes to Italy has the right to do so", he said.
Italy, along with Greece, has borne the brunt of the migration crisis, while other European Union countries such.
The 39-page document, obtained by Huffington Post Italia, also calls for a renegotiation of Italy's European Union budget contributions, an end to sanctions against Russian Federation and plans to dismantle a 2011 pension reform that raised the retirement age.
Di Maio charged against the Financial Times and unelected Eurocrats for undermining the prospect of an M5S-league government.
Carla Ruocco, a Five Star lawmaker, added: "We want balance and the wellbeing of the country within the European framework, we've always said this".