FAR 13.203 provides the purchase guidelines to answer this question. It says that micro-purchases shall be distributed equitably among qualified suppliers but they may be awarded without soliciting competitive quotations if the price is reasonable. Your applicable Governmentwide commercial purchase card program may add more to this, so you'll need to refer to those procedures as the final regulatory authority for using your GPC. As always, if competition is not going to happen, ensure to document and how the price is reasonable.