Lawyers for former House speaker Salvatore F. DiMasi and a former lobbyist urged a federal appeals court panel Tuesday to overturn their political corruption convictions, maintaining that a jury was wrong to convict them of a kickback scheme to help a software company win state contracts.

The lawyers argued that the federal judge who oversaw their clients’ trial in 2011 failed to correctly instruct jurors on laws relating to lobbying and the standards under which lobbyists can work in Massa­chusetts. The lawyers said that what ­DiMasi and his associates were accused of constituted lawful lobbying in the state.