Germany's energy regulator said the Nord Stream 2 pipeline must show it would not break competition rules by limiting which suppliers used it and could face a fine if it started pumping Russian gas to Germany without securing necessary approvals.
Nord Stream 2, a project led by Gazprom, which has a monopoly on Russian pipeline gas exports, will pump the fuel under the Baltic, bypassing Ukraine, which is embroiled in a long-running territorial dispute with Moscow.
Construction is completed and tests are underway, but the project has faced opposition from the United States and some European nations that say it will make Europe too reliant on Russian gas, which accounts for about a third of European needs.
Opponents also say Russia has applied pressure to try to speed up the German approval process by not supplying extra gas to Europe when the region faces an energy crunch as global gas demand surges and prices hit record levels.
The Kremlin says it is meeting its obligations.
German regulator Bundesnetzagentur (BNetzA) said late on Monday it had asked the pipeline operator, Swiss-based Nord Stream 2 AG, to show it was meeting all regulatory requirements before the pipeline entered service.
"This relates in particular to issues of non-discriminatory network access and the integration of the interconnector into the German market area," it said, a reference to rules that include ensuring the operator did not restrict access for other gas suppliers.
BNetzA, which said in September it had four months to complete certification, said it could not rule out that Nord Stream 2 operations could start soon, adding that all technical requirements had been met.