Banco Santander SA and Standard Chartered PLC are among at least five banks that have urged the European Union to reject a plan by global regulators that would force lenders to amass extra capital during boom times.

The capital plan is likely to place some banks at a competitive disadvantage and may heighten future financial crises, lenders told the European Commission. They urged the commission to either take a different approach than proposed by the Basel Committee on Banking Supervision or scrap the idea entirely.

"We are strongly opposed to its implementation until its impact has been more fully assessed," Standard Chartered said in a letter published on the commission's website. The bank has "serious concerns" about "the viability" of the plan.

The Basel committee has said that regulators should have the option of requiring banks to build up an additional capital buffer to curb excessive lending of the kind that led to the recent financial crisis. This so-called countercyclical buffer would also help lenders absorb losses in a recession and may amount to as much as 2.5% of a lender's assets, weighted according to their risk.

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