Brazil's stock exchange was scrambling today to finalise a cross-border deal with Nasdaq OMX ahead of a deadline of Sunday, after the country's government surprised investors with a new tax on equity trades.

New York-based Nasdaq has been exploring a deal with BM&F Bovespa, operator of Brazil's stock and derivative markets, since August. At the time, the exchanges said they would enter exclusive talks for 60 days in an effort to build a strategic and technological partnership. That period expires on Sunday.