The Nord Stream 2 project, a focal point of a wider discord between Moscow and Washington, plans to resume laying pipes on a 2.6 km stretch of the pipeline before the end of the year, and a Russian pipe-laying vessel has arrived at the construction site.

The alleged nerve agent attack on Kremlin critic Alexei Navalny in August has become the latest political controversy to hit the nearly-completed Nord Stream 2 gas pipeline, as Germany debates whether to halt the project as part of potential sanctions against Russia.

Led by Russia’s Gazprom with Western partners, the pipeline, which would double the capacity of the existing Nord Stream 1 link, is more than 90% completed and scheduled to operate from early 2021.

The project has split the European Union, with some members saying it will undermine traditional gas transit state Ukraine and increase the bloc’s energy reliance on Russia.

The United States, keen to increase LNG sales to Europe, also opposes the pipeline and has targeted some companies involved with sanctions.

Here are some key dates in Nord Stream 2’s development:

2011

November: Nord Stream 2’s forerunner, Nord Stream 1, a consortium mainly led by Gazprom, starts deliveries through a twin pipeline system to Europe under the Baltic Sea. The system’s 55 billion cubic meter (Bcm) capacity is equivalent to enough gas to heat 26 million households.

Gazprom and Western partners start looking into expanding the system with another two pipelines to add a further 55 Bcm of capacity. The project is estimated to cost 9.5 billion euros ($11.3 billion).

2015

June: Gazprom, Royal Dutch Shell, E.ON, OMV, BASF and ENGIE agree to build Nord Stream 2.

2016

March: Eight EU governmentsthe Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia and Romaniaobject to the project, warning it could have “potentially destabilizing geopolitical consequences.”

2017

April: Nord Stream 2 AG signs financing agreements with ENGIE, OMV, Shell, E.ON offshoot Uniper, and BASF’s subsidiary Wintershall.

2018

January: Germany grants Nord Stream 2 a permit for construction and operation in German waters and landfall areas near Lubmin in Mecklenburg-Vorpommern.

September: pipe-laying operations start in the Baltic Sea.

2019

January: the U.S. ambassador to Germany warns companies involved in the construction that they could face sanctions if they stick with the project.

December: Swiss-Dutch company Allseas suspends its pipe-laying activities in anticipation of President Donald Trump signing a defense policy bill, which includes sanctions on firms laying pipes for Nord Stream 2.

December: Trump signs the bill.

2020

January: Russian President Vladimir Putin says he hopes Nord Stream 2 will be finished by the end of first-quarter 2021. German Chancellor Angela Merkel says she believes the project is legitimized by European regulation and therefore should be completed.

May: Germany’s energy regulator declines to grant a waiver of EU gas directives to the operators of the Nord Stream 2 pipeline that require separate operators for the production, transport and distribution of energy on German territory.

May: An EU court throws out a challenge to EU gas rules from the operators of the Nord Stream 1 and Nord Stream 2 pipelines, saying it was up to individual members states to enforce them. Applying the gas rules costs time and money, but doesn’t question the pipeline operations as such.

June: Poland starts proceedings against Gazprom, alleging the company has not cooperated with the country’s anti-monopoly proceedings regarding Nord Stream 2.

August: Poland fines Gazprom 213 million zloty ($57 million) for a lack of cooperation in the matter.

Sept. 3: Pressure mounts on Merkel to reconsider the pipeline, after she says Navalny was poisoned with a Soviet-style nerve agent.

Sept. 7: Merkel’s spokesman tells German newspaper Bild am Sonntag she has questioned the project.

Sept. 8: Merkel and her economy minister play down the possibility of halting the pipeline

Sept. 11: The premier of the German state of Mecklenburg-Vorpommern, where Nord Stream 2 would come ashore, says the pipeline should not be used to punish Moscow over the Navalny case. Merkel wants to agree a response with EU partners.

Sept. 14: A Berlin government spokesman renews calls on Russia to explain the events surrounding Navalny’s illness.

Sept. 15: Data shows a Russian ship sailed for the Nord Stream 2 project’s supply base in Germany.

Sept. 23: The world’s largest group of shipping insurers says it will not insure vessels involved in the Nord Stream 2 and TurkStream gas pipeline projects because of the threat of U.S. sanctions.

Oct. 1: Denmark gives the Nord Stream 2 consortium permission to operate its Baltic Sea natural gas pipeline in Danish waters.

Oct. 6: Gazprom says it plans to complete Nord Stream 2 “as soon as reasonably possible.”

Oct. 7: Poland fines Gazprom more than 29 billion zlotys ($7.6 billion) for building Nord Stream without Warsaw’s approval.

Nov. 4: Gazprom files an appeal in a Polish court against that fine.

Nov. 11: Sanctions on companies facilitating the construction of the pipeline are included in the annual U.S defense bill, according to sources.

Nov. 28: Russia’s Nord Stream 2 says it plans to resume pipe-laying work on a 2.6 km stretch of the pipeline before the end of the year.

Dec. 1: The maritime authority in the German city of Stralsund informs shippers about pipeline-laying activities from Dec. 5 through Dec. 31 in the Baltic sea.

Dec. 3: U.S. lawmakers unveils a new U.S. defense policy bill, targeting companies and individuals providing help to the project.

Dec. 5: The Russian pipe-laying vessel Akademik Cherskiy stops near the construction site of the Nord Stream 2 gas pipeline in the Baltic Sea.