Speaking in Parliament on Thursday, Timmermans told MEPs that Poland had "come up with no concrete measures" to address EU concerns about the adoption of new laws in the country which, he said, violated the rule of law.
He was taking part in a debate Parliament's civil liberties, justice and home affairs committee on latest developments in the Commission's probe into the respect of the rule of law in Poland.
Timmermans reminded members that the Commission began investigating the situation in Poland in January 2016. It also launched an infringement procedure on 26 July.
The Dutch official said that the Polish President had subsequently agreed to scrap two of the four new pieces of legislation that the Commission objected to on the grounds that they posed a very significant threat to the independence of the Polish judiciary.
While he welcomed this, Timmermans said there appeared to be no such willingness to veto the two remaining laws or to restore the independence of the judiciary in Poland.
He said, "The Commission has now spent over a year spelling out our concerns to Poland. We have sent three lots of recommendations and started infringement proceedings but, despite this, the authorities have not come up with any concrete measures to address our continuing concerns."
He said that in its latest communication, on 28 August, Poland had asked for more clarification from the Commission, which Timmermans said was provided promptly.
"I have also invited ministers from Poland to come to Brussels to talk but have had no reply," he said.
"All they seem to want to do is attack the messenger, the Commission, and attack our competence and legitimacy on these issues."
The official added, "I cannot tell you today what our next step will be - that has to be discussed by the college - but the Parliament has an important role to play in ensuring that the rule of law is upheld in member states."
He said, "Our aim is not to impose sanctions on Poland. We remain open to dialogue but I want to stress today that we will use all the tools at our disposal in addressing this. Upholding our common values is vital and the rule of law is pivotal in this."
He stressed, "It is not our aim to interfere in a democratically elected government's right to implement judicial reform. But such reforms must respect the rule of law."
German S&D group deputy Birgit Sippel said, "It is noticeable that it is not just the Commission that is criticising the Polish authorities on this but the Polish people themselves."
She added, "The problem for the EU is knowing what to do about it. Our hands are tied to an extent and the infringement procedure can take years."
EPP group member Roberta Metsola noted that, "Poland calls this 'Brussels' interference' and brands those who dare to criticise these reforms as 'traitors'."