MOSCOW — After two decades of negotiations, Russia will finally join the World Trade Organization on Wednesday. The lower trade barriers that come along with membership will open up new opportunities for foreign companies to do business in Russia.

But American companies are guaranteed no such advantages — and may even face higher Russian tariffs than their competitors from other countries.

Because of broader policy concerns about the Kremlin’s crackdown on dissidents and its support for rogue governments, Congress has balked at the Obama administration’s request to grant Russia permanent normal trade relation status. That status is important since the W.T.O. requires that any country that seeks to benefit from it must apply the same trade rules to all member countries.

Major American exporters to Russia, like Caterpillar, Deere and General Electric, are worried about the potential impact on their business from the Congressional inaction. Across all sectors of the economy, Russia will lower import tariffs to 7 percent, from about 15 percent today, for the 155 countries in the trade organization. Although Russian officials say they do not have any immediate intention of applying discriminatory tariffs against American companies, they could legally do so at any time.