New Delhi, Aug. 6 -- The administration of US President Donald Trump is preparing to significantly tighten the H-1B visa regime by expanding an existing government fee to cover visa extension petitions, a move that could substantially increase costs for companies employing large numbers of foreign workers.

The proposal, now in the final stage of the federal rulemaking process, would require certain employers to pay an additional $4,000 fee for H-1B extensions and $4,500 for L-1 extensions, in addition to the fees already charged for new petitions.

If finalized, the rule would mark one of the most significant changes to H-1B filing costs in recent years, affecting technology firms, consulting companies and multinational employers that re...