Page "Conversion to Judaism" Paragraph 38

In general, branches of Orthodox Judaism consider non-Orthodox conversions either inadequate or of questionable halachic compliance, and such conversions are therefore not accepted by these branches of Judaism.

Conversely, both Conservative and Reform Judaism accept the stringent Orthodox conversion process as being valid.

Since 2008, Haredi Orthodox religious courts in Israel have been rejecting conversions from some other Orthodox rabbis, in addition to Reform and Conservative conversions, as not being stringent enough.