Okay, I am sorry to spam here so much on one evening but I have skimmed through the 90 or so pages of literary delight that are the ministry's proposal and wanted to share some of the interesting stuff. In general nothing shocking but since you're a teacher it's always good to know whats going on. (FYI that's the original in Bulgarian: http://bit.ly/KblRhQ )

-Paragraph 10 states, that international schools continue to operate under the agreement they were founded. (ACS is both Bulgarian and US certified, so I don't know which one would take presedence.)

The worrysome part might article 213 that states:
(1) The positions of pedagogical (that right?) specialists are filled by Bulgarian citizens... [blah, blah boring stuff]
(2) Then the second part talks about principals. 
[groan!]
(3) The positions of pedagogical specialists can also be taken by:
---1. Citizens of other member states. [i.e. of the EU]
---2. Other nationals who are appointed by force of an international agreement.
---3. Other foreign nationals with permanent residence.
[My read of this is: The Ministry of Education wants you to have a valid visa to employ you. The agency that grants the permanent residency visa wants you to have work to get you the visa. I.e. no one wants to take responsibility and as long as you find an employer you're fine.]

Nothing shoking and the draft was entered for review by a committee so things may change and stuff. But anyway, legislatively I'd be on the watchout for new laws concerning visa granting and work permits, not the education stuff.