Warned by CBP about traveling to the US using the wrong visa, but need to go again soon

Take that warning seriously, it is in their records (and in your interest).

But the immigration officer felt that I should be travelling on an L1 instead of a B1 since I am staying for longer duration in the US.

That's then the best advice for you, unfortunately we won't be able to better that one. After having assessed your travels and having interviewed you they advised that L1 is the proper category then please go ahead and discuss that with your employer and apply for an L1.

There is no point looking to interpret things differently after having been given a clear advice by the most relevant authority.

I can spend some time to find some authoritative resources to support my answer but all those resources say that the final discretion to let you in the US lies with the officer interviewing you at the port of entry. The advice that you received was exactly from that very officer.

Now I am required to travel to US again for a week in 2nd week of September and I am not sure if this qualifies as a similar travel. I am travelling on behalf of the same organization to visit a different client in a different city and this time staying only for a maximum of 1 week.

It does qualify to be the same situation, I wouldn't risk thinking oh he just thought i was staying for too long.

Take their advice without any grain of salt.

My worthless 2 cents?

I have stayed for around 63 days this year in the US

They are right. 63 days business activity in only 2 trips in only 8 months does seem to be beyond what B-1 entitles an alien. I think the supervisors are going to say the same thing.

You need to call the CBP immediately at +1 202 325 8000, ask for a supervisor (tell them it's a complicated and serious matter and that you must be 100% sure to receive the right answer).

Tell them your passport number and last admission number (can be looked up here), and tell them exactly what the officers in New York told you.

Ask them to check their records (if possible), and ask if you should apply for an L-1 or can keep using your B-1/B-2. (Of course, describe exactly what you'll be doing.)

Then insist that they write you a clear, detailed E-Mail confirming what you've said on the phone, either so you can show your employer (if they say you should get an L-1) or so you can show local CBP officers (if they say you can keep using your B1/B2 visa).

As you probably known, there has been a lot of fraud involving H1-B visas, and the US government is (sort-of) cracking down on it.

As a result, various outsourcing companies have been bringing in half-priced foreign workers under the B-1 visa. This has, predictably, caused people coming here on B-1 visas to get extra scrutiny.

What happens next depends a lot on what exactly you are doing. If it is sales meetings or training, then you need to carry documentation of what the exact purpose of your visit shall be.

If you are going to be writing code for a database or for a user interface, then you will need to get an L-1 visa.

My personal opinion is that you need to talk to an immigration lawyer. If a Border Agent gets the idea that you are traveling on funny papers, then they will put you on The List, probably for the rest of your life.