Workers want to protest the sale of company assets and former president Lula's arrest.
The Dutch oil company is paying Pampa a total of US$125mn for assets that include more than 250 service stations and the Ricardo Elicabe refinery.
If negotiations are successful, it will be the Russian firm's debut in Latin America.
Now, the Norwegian group expects to close the deal by the end of May.
The new regulation is part of energy ministry's RenovaBio program for the development of the biofuels industry.