Mumbai: As New Delhi and RBI explore ways to tame the rupee, Indian banks have urged the regulator to lift a guarantee restriction to attract the diaspora money.Banks, which the RBI sounded out last week on a possible foreign currency non-resident (FCNR) special deposit scheme to increase dollar supply, told the central bank to relax its directive on standby letter of credit (SBLC)-a credit comfort or guarantee-that some of the large Indian banks had given to offshore banks in 2013. The SBLC paved the way for overseas banks to liberally lend to NRIs who placed the borrowed funds as FCNR deposits."RBI didn't say it was opening a FCNR window. In fact, banks said while FCNR may be a quicker route to bring in dollars, it would be expensive. Subsidising the hedging cost of dollar bonds and external commercial borrowings by PSUs and corporates may cost less though dollar inflows could take longer. We get a sense the RBI and the government want to be ready with all information so that the rollout, if needed, can be quick. They don't want any step to be seen as a panic reaction," a senior banker told ET. "If oil stays around $90, they may not take big measures," he said.The SBLC curb, a forgotten issue, cropped up when RBI sought banks' response to a FCNR plan. In 2013 and earlier, NRIs took huge leverage-often four to ten times-of the amount chipped in to make risk-free return on the difference between the borrowing cost and return from the FCNR facility. Say, an NRI in Dubai would chip in $100,000, borrow another $900,000 from a UAE bank to place $1 million as deposit.