Kosovo's PM Albin Kurti first announced the implementation period to be over at the start of September but has later extended the deadline to 31 October.
Tensions are high over car plates between the government of Kosovo and the ethnic Serbs in the Serb-majority municipalities.
Pristina refuses to delay the end-of-month deadline, demanding that all those residing in Kosovo swap Serbian-issued car number plates for Kosovar ones.
Kosovo, which is predominantly ethnic Albanian, has sought to compel Serbs to accept Pristina's authority in routine bureaucratic matters since it declared independence in 2008.
Prior to the declaration, the former Serbian province was a UN protectorate since the 1999 NATO military intervention aimed at stopping the ethnic cleansing and repression of Albanians by the Belgrade forces under the control of strongman Serbian President Slobodan Milošević.
Its independence has been recognised by the US and all but five European Union countries, but Serbia, backed by its allies Russia and China, refuses to do so -- claiming the declaration of independence was done unilaterally -- as do most ethnic Serbs inside Kosovo.
After the withdrawal of Serbian forces, the authorities in Belgrade have set up parallel state services -- including car registration offices -- in other parts of the country.
Pristina contests the validity of those licence plates, claiming that the switch to Kosovo-issued plates is in accordance with the 2011 Brussels agreement between the two sides.
Few switch to new plates despite calls from Pristina
Despite the flare-up over the issue, the US government spokesman Ned Price said the White House is confident that both Kosovo and Serbia can reach an agreement peacefully in the coming days.
Kosovo's Prime Minister Albin Kurti says the country is simply exercising its right to sovereignty.
"We have already postponed the deadline. Instead of being on 30 September, the last date is 31 October where all citizens of Kosovo who have vehicles with outdated plates will be able to convert them into legitimate licence plates."
"I call on all citizens to convert the cars with those licence plates into legitimate ones," Kurti said.
Some 50,000 people living in Serb-majority areas of the north use registration plates issued by Serbian authorities in defiance of the Kosovar institutions.
When the announcement came back on 1 September, NATO peacekeepers were deployed in northern Kosovo to calm tensions after ethnic Serbs put up roadblocks in protest of the Pristina decision.
Domestic press in Kosovo reported that the number of those who have switched to Kosovo-issued car plates is in the mere dozens.
In late September, Kosovo Interior Minister Xhelal Sveçla claimed that at least three ethnic Serbs were targeted with property destruction after making the switch, two of them being officers of the Kosovo police.