Russia's environmental agency has asked for an extra month to probe the Sakhalin-2 oil and gas project and has warned it may prosecute its operator.
Shell's giant oil and gas project is off the island of Sakhalin
Natural resources minister Yuri Trutnev said that environmental breaches at the project, led by Anglo-Dutch energy giant Shell, broke five criminal codes.
Earlier this week Russia reiterated that it could withdraw Shell's licence for the $22bn (£11.7bn) project.
But operator Sakhalin Energy insisted the probe would not delay its launch.
"The current situation could lead to some delays in completing certain elements of the project, but it will in no way lead to a delay in the project as a whole," said chief executive Ian Craig.
"Every problem will be dealt with in the correct manner and in full partnership, openness and transparency with the supervisory agencies."
Russia's environmental agency, RosProdNadzor, has said it needs more time for its investigations because the scheme differs significantly from original plans.
However, some analysts said the way the Sakhalin issue had been handled was designed to strengthen the government's position in renegotiating the development of the field.
The aim, they said, was to get Russian energy giant Gazprom into the project - the world's largest single oil and gas scheme - as a partner.