B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Confusion; Situational Awareness; Communication Breakdown
ATC Issue All Types; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued Advisory / Alert
Procedure; Human Factors
We were being vectored from the south at 2000' MSL to intercept the LOC course for BWI Runway 10 ILS. Ceilings were ragged between about 1700'- 2000'.  We were told to maintain 2000' until LOC intercept then cleared for the ILS.  It looked to me as though we would intercept at COLUM which shows 2500' on the approach chart. The Runway 10 ILS has no DME; I relied on the CDU to indicate that we had passed COLUM. As we got VOR/LOC I descended to 1500' to intercept GS at JEANS.  Right as we got to 1500' we got an altitude alert from Approach. I don't recall the exact verbiage; but it was something like; 'Company # minimum MDA is 2000'.' Since we were approaching the FAF; we stayed at 1500' and intercepted the G/S.  That was the only fallout that we received.  Landed normally and taxied to the gate.
The reporter stated the procedure as executed that day he has flown many times and was confused by the call. In retrospect; he believes that because of low ceilings and actual IMC conditions; the Controller was busy and simply became confused possibly by the minimum vectoring altitude in that area. The crew was very confused by the event.
[Report narrative contained no additional information.]
A B737 crew flying the BWI Runway 10 ILS descended to 1;500' inside COLUM on the localizer as per the ILS approach chart but were to told by PCT the minimum MDA altitude 2;000'. The crew could not find the basis for that statement.