During each status phase each player with an active tread agreement has to pay a TG to the minister of Commerce.

But what to do if I have no TG?

Exhaust planets?

Marechallannes said:

You just don't pay. If you don't have any, you don't give any.

When this law is in play, players tend to spend their TGs first; the minister often gets nothing. However, this isn't necessarily a bad thing for the minister, because it does force them to spend rather than save, and the minister can use this to his advantage (as he can save without reprecussion, usually)