The STRTCPFTP command has several parameters (PORT, SECCNN, DTAPROT) that initiate a secure connection from the client side. The FTP manual describes these parameters: http://publib.boulder.ibm.com/infocenter/iseries/v5r3/index.jsp?topic=/rzaiq/rzaiqrzaiqclientsession.htm
Make sure you understand whether or not “the bank” understands what they’re talking about. There is ftps and there is sftp, and there are different kinds of both of those. Usually, “the bank” won’t know any more than you do. They will typically only know what they’ve been told about what they run and possibly won’t realize there are alternatives with names that sound very similar.
What that means is that you’ll want to find out what the technical specs are. From those it’ll be fairly easy to determine which alternative you’ll want to use; possibly even what you’ll need to install.