I believe this is half-toned and warped. One of the comments give a link to another case where half-toning is used.
We try here something resembling. Do not expect even a nearly exact copy - complex stuff like this is very hard to repeat.
In illustrator we have some 50% grey shapes (a circle + outlined letters). On the top there's a pattern of black curves. It's made with blending.
Next we give a heavy gaussian blur to the grey shapes:
Black curves get also gaussian blur, but lighter to keep them visible. Blur radius is about half of the stroke width.
Half-toning is made by tresholding everything. Unfortunately we haven't it in Illustrator. We must rasterize all and make black-white live tracing instead.
Rasterizing must be in high resolution, a white background is added:
Live tracing to BW needs careful settings. White can be rejected here to get transparent background:
Higher white treshold leave the curves visible:
Now it's easy to decide improvement possiblities:
We had solid grey shapes. Gradient fill would give variation to resulted line widths.
Having part of the shapes blurred less and others more gives more variation (less blur => more defined shape edges)
Envelope distortion or other warping to shapes before half-toning is possible without affecting resulted line densities and thicknesses
Warping after half- toning affects line densities. Illustrator has envelope distortion and special warping tool. We skip them and try Photoshop. We copy the result to Photoshop as a new pixel layer. In PS we have prepared a high resolution image with white background for this:
We make a few pushes and pulls with the Liquify filter, then we invert all colours and get our final result:
Here's another random attempt. There's applied different blurs and shallow gradient fills to the grey shapes.
As said, not really the same as your example, but maybe gives a starting point. Your example has somehow ultra clever left-right antisymmetry, where line widths grow to up in left and to down in right.