After taking power in Romania, two months after the elections, the Government issued a very controversial ordinance bill that weakens anti corruption. This led to massive protests and issuing of another ordinance bill that cancelled the first one.
If it had not been cancelled, several notorious corrupts would have benefit from this ordinance as indicated in this article (Romanian text). They include both heads of Parliament Chambers and normal members of the Parliament.
President of the European Council, Donald Tusk, summoned the Prime Minister to provide explanation about all these, before the Parliament had to examine the bills (they must be approved or rejected within a time frame):
President Tusk underlined the need to advance in the fight against corruption, safeguard the significant progress achieved and ensure its irreversibility, in line with the high expectations of Romanian society and the EU's values.
Eventually, both bills were rejected by the Parliament. Some analysts argued that protests alone, although massive for several days, could not be the only cause and EU officials must have had some influence.
Question: How can European Union officials influence such political decisions? What are the political mechanisms to persuade local politicians to change their minds?
I know about financial sanctions, but they come after a relatively long bureaucratic process (infringement proceedings).