This letter was written on the debian-science mailing list, see the following thread:
Dear <upstream author>:
We are working on creating a set of packages of free software related to molecular and computational biology for the Debian GNU operating system . We would love to create a Debian package of <software in question> so that it can be used by the growing number of biologists who use Debian as a work platform. This will make installation of the software very fast and easy. We would maintain the package, and send bug reports to you.
Unfortunately, we could not find the licence of <software in question> in either website nor in its sources. In the countries which have ratified the Berne convention on copyright , its redistribution is not permitted if not allowed explicitely by a license.
We are therefore wondering if you would consider releasing <software in question> as free software. This would allow us to package it for distribution along with the rest of the Debian system. The ability to include software in Debian depends on consistency of its license with the Debian Free Software Guidelines .
Debian distributes software packages with many different licenses, so there is no single Debian license. Some of the more common free software licenses are the GNU GPL, the Lesser GPL, the revised BSD, Artistic, MIT and Mozilla licenses. You might wish to read through a few of them, available here: http://www.opensource.org/licenses/
Unless you have specific needs, we would strongly recommend that you choose a widespread licence, as there is a broad consensus on how they should be interpreted. For free software, the GNU General Public Licence (GPL)  and the revised licence of the Berkeley Software Distribution (BSD)  are very popular choices. Their main difference is that the GPL insists on derived work to be free software as well, while the BSD licence allows derived work to be distributed with other code for which the source code is not freely available.
It is important that none of these licences contains restrictions on commercial or non-commercial uses. A common case is software which is available for free only for academic users; this is not free software. While such licences are useful in some cases (such as collaborations with for-profit partners), we would like to discourage their use if there is no economic rationale for doing so. In particular, our current effort is to create a distribution of free software for biologists, from sequencing genomes to the modelling of interaction networks, and we would like to avoid distributing together software with and without restrictions on commercial use, in order to reach the broadest possible range of users.
Finally, let us make it clear that we are not speaking on behalf of the Debian Project. However, we would be very happy to be able to package <software in question> for Debian along with the rest of the packages related to molecular and computational biology that we are distributing.
Thank you for your consideration,
Remember to thank upstream profusely if they re-license under a DFSG-compatible license. Even if they refuse, thank them for their time and consideration of your request.